PIP: 100 patients received 150 mg of depo-medroxyprogesterone acetate (DMPA) supplied as Depo-Provera, between Days 1 and 5 postpartum and then at 3-month intervals. Vaginal cytologic smears and endometrial biopsies were obtained 6 weeks and 3 months after the first injection and then 3 months following each subsequent injection during a 1 year study period. Of the 100 patients, 82 received at least 1 subsequent injection. Of these 22 received injections 1-4 weeks late. At the end of 1 year 43 patients had continued the treatments and 31 continued longer. 24 stopped for medical reasons, mostly irregular vaginal bleeding. Others had moved away or lacked transportation to the hospital. By the end of the year 77% of the patients were amenorrheic. About as many lost as gained weight. Of 275 endometrial biopsies obtained from 86 patients none showed a secretory type of endometrium. 6 weeks after first injection 44% of biopsies showed a minimally proliferative type of endometrium. Later this type of reaction became less frequent and more showed a quiescent type. At 1 year 40% of biopsies showed an atrophic endometrium. In 241 vaginal smears both the mean and median karyopyknotic indices were low. Resumption of spontaneous ovulation occurred at prolonged and unpredictable intervals after stopping therapy. Pregnancy occurred in 6 women, a failure rate of .51% per 100 woman-years of use.