Clinical research was carried out to assess the effects of 2 longacting injectable contraceptives on the ovaries and uteri of female virgin rats. 2 different doses of DMPA (depo-medroxyprogesterone acetate) and NE (norethisterone enanthate) and 2 control substances were used in the study. The laboratory procedures employed are explained and the results tabulated. Subcutaneous injections of a single dose (ranging from 5-20 mg/kg) of both substances caused reduction in the number and diameter of corpora lutea and an increase in the number of atretic and cystic follicles in the ovary. Histologic examination of the endometria showed low cubiodal cells with sparse distribution of low columnar cells, glands with atrophic changes, and compact uterine stroma with or without patches of edema. Reduced thickness of the uterine wall and endometrium were observed among the drug treated animals. Results of this study suggest regressive and atrophic changes in the ovary and endometrium.