Hyperinsulinemia has been accused to be among the underlying causes of certain endocrinopathies such as polycystic ovary syndrome and hyperthecosis. In this study, it was found that hyperinsulinemia altered the histological structure of the rat ovaries. There was increase in the thickness of the germinal epithelium of the capsule of the ovary and that of the theca folliculi of the Graffian follicles. There was a decrease in the number of all growing follicules and corpora lutea and there was an increase in the number of the atretic follicles. Administration of human chroionic gonadotropin was seen to improve the occurring changes and possibly to exert a protective effect on the ovaries.