A double-blind, placebo-controlled, randomized trial, was carried out in 120 Norplant users to evaluate the effect of mifepristone, 100 mg/day administered for 2 consecutive days every 30 days, on the vaginal bleeding pattern. Treatment was given from months 2-7 of implant use. Volunteers recorded bleeding and spotting days, during treatment and for the ensuing 6-month period. During treatment, women on mifepristone recorded the same frequency of bleeding/spotting episodes but significantly less prolonged bleeding episodes than placebo controls (mean +/- SD: 11 +/- 3 vs. 22 +/- 23 days) and their total number of bleeding days was 35% lower than in the placebo group. After the end of mifepristone use, bleeding patterns were similar in both groups. One pregnancy occurred in the mifepristone-treated group, in month 6 of treatment, the outcome was a healthy male baby. We conclude that intermittent administration of mifepristone can offer a clinically significant improvement of the vaginal bleeding pattern in Norplant users.