Total of 5578 male merinos were evaluated for cryptorchidism and testis hypoplasia in HAYMAREN -Konya, KAE - Bandırma. and TIGEM - Altınova, born in 1993 and 1994, Polatlı and Karacabey in 1994. The incidence of cryptorchidism was 10.3 and 8.5% in Haymaren - Konya, 23.2 and 7.1 %in KAE - Bandırma, 5.7 and 2.9% in Altınova, N/A and 5.6 % in Polatlı, N/A and 8.5% in Karacabey in 1993 and 1994, respectively. The ineidence of testis hypoplasia was 5.3 and 6.3 % in Haymaren - Konya, 5.7 % and N/A in KAE - Bandırma, 6.7 % and N/A in Altınova in 1993 and 1994, respectively. 67.7 % bilateral and 32.3 % unilateral, of which, 83.2 % was right cryptorchid testes were detected. 69.6 % bilateral and 30.4 % unilateral, of which, 64.7 % left hypoplastic testes were detected.Certain nummer of rams with cryptorchid and hypoplastic testes was selected for plasma levels of testosterone, LH, FSH and spermatologic evaluation. When the rams reached 1 year of age, they were terminated, and the testes were subjected to microscopic and macroscopic evaluations. Tubulus seminiferus contortuses were covered with foetal sertoli cells, small in diameter in cryptorchid testes. Spermatogenesis ceased at spermatid and secondary spermatocyte phases in light and moderate hypoplastic testes, respectively. Bilateral moderate degree hypoplasia was characterised by azoospermia. While plasma testosterone levels were within normal limits orhighly increased, LH levels were highly increased in cryptorchid testes. FSH levels were found to be highly increased in cryptorchid and hypoplastic testes.ln this study, the incidence of cryptorchidism was found to be high and attributed to the hereditary factors, which was thought that would be decreased by selection. Pathological changes found was not to be detectable until sexual maturity. lt was concluded that the rams must be at least 12 months old in order to detect the hypoplastic testes.