Estrogen   and   progesteron   are  the   most  important  female   sexual

   hormons which is administrated for  the treatment of some women diseases

   and   also   are  used  in contraceptive pills. Administration of female sexual

   hormons during  critical  period  of  embryonic  development may produce

   malformations. In this study which was undertaken during 1998-99 in biology 

   department, school of sciences, Ferdowsi university of Mashhad.

         The incidence of motor limbs abnormality due to estradiol administration

   during  the  rat  embryonic development  was investigated. Three groups of

   pregnant wistar  rats  were  exposed  to  0.15mg/kg  estradiol valerate via a

   single intramuscular injection on one of the following gestational days;12,14

   or 16  of experimental groups 1, 2 and 3 respectively.  The control pregnant

   rats(group 4), were recieved physiological serum in the same manner. All of

   pregnant   rats  were  sacrificed  on  the  last  day   of  pregnancy and their

   fetuses were collected, counted and examind for limbs abnormalities.

         Our    results    indicate   that    in   comparison    with    control  group, in

   experimental groups the size of litters significantly reduce and the incidence

   of  malformations, especially  in experimental  group 1 are significantly high.

   The   markedly    limbs   malformations   are   syndactyly ,  tetraductyly  and

   phocomellya.

         Since the critical   period   of  rat   motor  limbs embryonic development 

   is between 11to 13th post-mating day, the estradiol administration in group  

   1  probably   by interrupting   the   programed  cell  death  phenomena   or 

   blocking the chemical receptors in limb bods produce limb abnormalities.