The present study was undertaken to elucidate (1) the relationship between plasma concentration of medroxyprogesterone acetate (MPA; Clinovir) administered by the PO and the IM routes; and (2) the relationship between dose and plasma concentration of MPA. Nineteen patients entered the study. In each patient the plasma concentration was monitored after a single PO and IM administration of MPA at the following dose levels: 100 mg (5 patients), 400 mg (5 patients), 800 mg (5 patients) and 1,200 mg (4 patients). The time interval between PO and the IM administration was 1 week. The results show (1) a very large interindividual variation in plasma concentration; (2) increasing plasma concentration with both PO and IM dose; (3) after the IM administration plasma levels are steady or increase slightly within the test period; (4) after the oral administration the concentration increases rapidly to reach a peak before 2-7 h and subsequently decreases again, peak concentrations being 2-10 times higher than after IM administration; and (5) within the test periods the plasma concentration x time (0-168 h) is comparable with the two methods of administration.