The effect of a single dose of 150 mg depomedroxyprogesterone acetate (DMPA) on pituitary, ovarian, and endometrial function was assessed in relation to the peripheral levels of the compound in 8 women. The levels of DMPA, follitropin (FSH), lutropin (LH), prolactin, estradiol (E2), and progesterone (P) were measured 3 times/week during a pretreatment (control) cycle and then daily during postinjection weeks 14-17, 22-25, and 30-33. An endometrial biopsy specimen was obtained during postinjection weeks 17, 25, and 33. In 3 of 8 subjects the daily hormone assays carried out during postinjection weeks 30-33 indicated anovulatory periods; in these subjects, peripheral blood was drawn daily during postinjection weeks 46-49 and a 4th endometrial biopsy was taken during week 49. Plasma DMPA levels during the 14th postinjection week varied between 0.90 and 2.24 nmol/1, declined gradually, and became undetectable between weeks 17-24 (4 cases) or some time after week 33 (the other 4 cases). No correlation was found between the time when DMPA levels became undetectable and the obesity index.