SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                                    ________

                                    FORM 6-K

                        REPORT OF FOREIGN PRIVATE ISSUER
                      PURSUANT TO RULE 13A-16 OR 15D-16 OF
                       THE SECURITIES EXCHANGE ACT OF 1934

                           For the month of May, 2005

                                  Serono S.A.
                                 --------------
                              (Registrant's Name)

                            15 bis, Chemin des Mines
                                 Case Postale 54
                                CH-1211 Geneva 20
                                  Switzerland
                      -----------------------------------
                    (Address of Principal Executive Offices)

                                    1-15096
                                   ----------
                              (Commission File No.)

     (Indicate by check mark whether the registrant files or will file annual
reports under cover of Form 20-F X  or Form 40-F.)

     Form 20-F  X   Form 40-F
               ---            ----

     (Indicate by check mark if the registrant is submitting the Form 6-K in
paper as permitted by Regulation S-T Rule 101 (b)(1).) ____

     (Indicate by check mark if the registrant is submitting the Form 6-K in
paper as permitted by Regulation S-T Rule 101 (b)(7).)   ______

     (Indicate by check mark whether the registrant by furnishing the
information contained in this form is also thereby furnishing the information to
the Commission pursuant to Rule 12g3-2(b) under the Securities Exchange Act of
1934.)

     Yes       No   X
         ----      ----

     (If "Yes" is marked, indicate below the file number assigned to the
registrant in connection with Rule 12g3-2(b): 82-______)



Genmab                                                                    Serono


Media Release



FOR IMMEDIATE RELEASE
---------------------


                   SERONO AND GENMAB SIGN WORLDWIDE AGREEMENT
                     TO DEVELOP AND COMMERCIALIZE HUMAX-TAC

   HUMAX-TAC MAY HAVE THERAPEUTIC POTENTIAL IN THE TREATMENT OF T-CELL MEDIATED
                                    DISEASES


GENEVA,  SWITZERLAND  AND  COPENHAGEN,  DENMARK  -  MAY  2,  2005  -
Serono  (virt-x:  SEO  and  NYSE: SRA) and Genmab A/S (CSE: GEN) announced today
that  they  have  signed an agreement under which Genmab grants Serono exclusive
worldwide  rights  to develop and commercialize Genmab's HuMax-TAC.  The product
is  a  fully human monoclonal antibody targeting the TAC antigen - also known as
CD25,  or  the  interleukin-2  receptor  alpha  subunit  (IL-2Ra)  -  which  is
overexpressed by activated T-cells.  By inhibiting the proliferation of T-cells,
HuMax-TAC  may  have  therapeutic  potential in the treatment of T-cell mediated
diseases, such as autoimmune disorders, inflammatory and hyperproliferative skin
disorders,  as  well  as  acute transplant rejection.  HuMax-TAC is currently in
pre-clinical  trials.

Under  the agreement, Genmab will receive an upfront payment of US$2 million and
is entitled to potential milestone payments of up to US$38 million and royalties
on  sales  from  any  eventual commercialization of the product.  Serono will be
responsible  for  all  future  development  costs  for  HuMax-TAC.

"We  are very pleased to enter into this partnership with Serono for HuMax-TAC,"
said  Lisa  N.  Drakeman,  Ph.D.,  Chief  Executive Officer of Genmab, "Serono's
wealth  of  knowledge  and expertise in developing and marketing products can be
applied  to  the  ongoing  development  of  HuMax-TAC."

"We  are  committed  to  the  development  of  novel  therapeutics  to  fulfill
significant  unmet  medical  needs,"  said  Timothy  N.C.  Wells,  Ph.D, Head of
Research  at  Serono.  "We  believe that HuMax-TAC brings a new dimension to the
treatment  of many of the key diseases where Serono has a scientific and medical
interest."


                                                                             1/3

                                       ###


Genmab  forward  looking  statements
This  press  release  contains  forward looking statements. The words "believe",
"expect",  "anticipate",  "intend"  and  "plan" and similar expressions identify
forward-looking  statements. Actual results or performance may differ materially
from  any future results or performance expressed or implied by such statements.
The  important  factors  that  could  cause our actual results or performance to
differ materially include, among others, risks associated with product discovery
and  development,  uncertainties  related to the outcome and conduct of clinical
trials  including  unforeseen  safety  issues,  uncertainties related to product
manufacturing,  the  lack of market acceptance of our products, our inability to
manage  growth, the competitive environment in relation to our business area and
markets,  our  inability to attract and retain suitably qualified personnel, the
unenforceability  or  lack  of protection of our patents and proprietary rights,
our  relationships  with  affiliated  entities,  changes  and  developments  in
technology  which may render our products obsolete, and other factors. Genmab is
not under an obligation to up-date statements regarding the future following the
publication  of  this  release;  nor  to  confirm such statements in relation to
actual  results,  unless  this  is  required  by  law.


                                       ###



Serono  forward  looking  statements
Some  of  the  statements  in  this  press  release  are  forward  looking. Such
statements  are inherently subject to known and unknown risks, uncertainties and
other  factors  that  may  cause  actual results, performance or achievements of
Serono  S.A.  and  affiliates  to be materially different from those expected or
anticipated  in  the  forward-looking statements. Forward-looking statements are
based on Serono's current expectations and assumptions, which may be affected by
a  number  of  factors, including those discussed in this press release and more
fully  described  in  Serono's  Annual  Report  on Form 20-F filed with the U.S.
Securities  and Exchange Commission on March 16, 2005. These factors include any
failure  or  delay  in  Serono's ability to develop new products, any failure to
receive  anticipated  regulatory  approvals,  any  problems  in  commercializing
current  products  as  a  result of competition or other factors, our ability to
obtain  reimbursement  coverage  for  our  products,  the  outcome of government
investigations and litigation and government regulations limiting our ability to
sell  our  products.  Serono has no responsibility to update the forward-looking
statements  contained  in  this press release to reflect events or circumstances
occurring  after  the  date  of  this  press  release.




                                       ###


                                                                             2/3

ABOUT GENMAB A/S
Genmab A/S is a biotechnology company that creates and develops human antibodies
for  the  treatment  of  life-threatening  and debilitating diseases. Genmab has
numerous products in development to treat cancer, infectious disease, rheumatoid
arthritis  and other inflammatory conditions, and intends to continue assembling
a  broad  portfolio of new therapeutic products. At present, Genmab has multiple
partnerships  to  gain  access  to  disease  targets  and  develop  novel  human
antibodies  including agreements with Roche and Amgen. A broad alliance provides
Genmab  with  access  to  Medarex,  Inc.'s  array  of  proprietary technologies,
including  the  UltiMAb(TM)  platform  for the rapid creation and development of
human  antibodies  to  virtually  any disease target. Genmab is headquartered in
Copenhagen,  Denmark,  and  has  operations  in  Utrecht,  The  Netherlands, and
Princeton,  New  Jersey  in  the  US.  For  more information about Genmab, visit
www.genmab.com.
---------------


ABOUT SERONO
Serono  is  a  global biotechnology leader.  The Company has eight biotechnology
products,  Rebif(R),  Gonal-f(R),  Luveris(R),  Ovidrel(R)/Ovitrelle(R),
Serostim(R),  Saizen(R),  Zorbtive(TM) and Raptiva(R).  In addition to being the
world  leader  in  reproductive  health,  Serono  has strong market positions in
neurology,  metabolism  and  growth and has recently entered the psoriasis area.
The  Company's  research programs are focused on growing these businesses and on
establishing  new  therapeutic  areas, including oncology.  Currently, there are
approximately  30  ongoing  development  projects.

In  2004,  Serono  achieved  worldwide revenues of US$2,458.1 million, and a net
income  of  US$494.2 million, making it the third largest biotech company in the
world.  Its  products  are  sold  in over 90 countries.  Bearer shares of Serono
S.A.,  the  holding  company,  are  traded  on the virt-x (SEO) and its American
Depositary  Shares  are  traded  on  the  New  York  Stock  Exchange  (SRA).

FOR  MORE  INFORMATION,  PLEASE  CONTACT:

SERONO

CORPORATE MEDIA RELATIONS:     CORPORATE INVESTOR RELATIONS:
Tel:  +41  22  739  36  00     Tel:  +41  22  739  36  01
Fax:  +41  22  739  30  85     Fax:  +41  22  739  30  22
http://www.serono.com          Reuters:  SEO.VX  /  SRA.N
---------------------
                               Bloomberg:  SEO  VX  /  SRA  US

MEDIA  RELATIONS,  USA:        INVESTOR  RELATIONS,  USA:
Tel:  +1  781  681  2340       Tel:  +1  781  681  2552
Fax:  +1  781  681  2935       Fax:  +1  781  681  2912
http://www.seronousa.com
------------------------


GENMAB

Helle Thalund Husted
Director, Investor Relations
T: +45 70 20 27 28
F: +45 70 20 27 29
E: hth@genmab.com

UltiMAb(R) is a registered trademark of Medarex, Inc.
HuMax(R) is a registered trademark of Genmab A/S
HuMax-CD4(TM) is a trademark of Genmab A/S


                                                                             3/3

                                   SIGNATURES

     Pursuant to the requirements of the Securities Exchange Act of 1934, the
registrant has duly caused this report to be signed on its behalf by the
undersigned, thereunto duly authorized.



                                   SERONO S.A.
                                   a Swiss corporation
                                   (Registrant)



May 2, 2005                         By:  /s/ Stuart Grant
                                         ------------------------------
                                         Name:  Stuart Grant
                                         Title: Chief Financial Officer