One hundered and twenty adult female albino rats were divided intofour groups to study the pathologic change which induced due to longadministration of high and Iow dose of sex hormones (estrogen,progesterone and their combination).Experimental groups were treated as follows:Group (gp.) I: (subgp. A and B) subcutaneous injected with 0.1 mgand 0.05/rat of estrogen respectively and (subgp. C and D) orally received0.1 mg and 0.05 mg per rat of estrogen respectively.Group 1/: (subgp. A and B) orally received 2.5 mg and 1.5 mg/rat ofprogesterone respectively.The present study was carried out at the sheep experimental farmbelonging to the Department of Animal production ,Faculty of Agriculture(Moshtohor) , Zagazig University (Benha) . The radioimmunoassy forprogesterone and oestradiol-l Zf in blood plasma was carried out in BiologyDepartment, Pyramid Research Institute for animal Reproduction .The study was conducted during the period from September (1994) toAugust (1995). A total number of 180 ewes of2 - 5 years old were used in thestudy . Throughout this period of the study 45 ewes were conserved eachseason and divided as follows:Group (1) of 10 ewes and treated with 100 J..I.g Gn-RH (Fertagyle) ;group (2) of 10 ewes and treated with 200 /-lg On-RH; group (3) of 10 ewesand treated wi th 1 mg oestradiol benzoate (F olon -5) ; group (4) of 10 ewes andtreated with 3 mg oestradiol benzoate, group (5) of 5 ewes and injected with2 ml placipo as control .Half number of the first four groups was serviced atfirst heat post-treatment while the other half was serviced at the second heat.On statistical analysis, the obtained data showed the following results:J) The time elapsed from treatment till heat signs appearance:There was no significant variation in the time elapsed from treatment tillthe heat appearance among the different seasons and different treatments. Inewes treated with 100 and 200 ug Gn-RH the overall means were 72.18 ± 0.96and 70.38 ± 2.42 hours respectively. The mean durations were 70.80 ± 2.72,73.90 ± 1.98,70.20 ± 2.02 and 73.75 ± 1.16 hours for ewes treated with 100J..l.gGn-RH,and it was 68.80 ± 2.46, 74.60 ± 1.37 , 62.80 ± 0.32 and 75.30 ± 1.69hours for ewes treated with 200 J..I.g Gn-RH during Autumn, Winter, Spring