This 12-month, double-blind, randomized study evaluated the safety and efficacy of topical minoxidil in the treatment of male pattern baldness. Three formulations were compared: 2% minoxidil solution, 3% minoxidil solution, and placebo. After 4 months all placebo patients crossed over to treatment with the 3% solution. Of the 96 patients randomized into the study, 79 were evaluable at month 12; 25 of these were in the 2% minoxidil group, 24 were in the 3% minoxidil group, and 29 were in the placebo-to-3% solution switchover group. At monthly intervals a hair count was obtained within a 1-inch diameter area on the scalp vertex. In addition, a gross visual estimate of the degree of new hair growth over the entire balding area was made independently by the investigator and the patient. At the end of 4 months there was significant regrowth of nonvellus (terminal and indeterminate) hairs in the patients using the 2% and 3% solutions (p = 0.0001). The mean nonvellus hair count at month 4 was 162.8 in the 2% minoxidil group, 155.4 in the 3% minoxidil group, and 107.1 in the placebo group. The mean increase in the 2% and 3% treatment groups was 58.2 and 48.8, respectively, whereas the mean increase in the placebo group was 4.0. Total hair counts at month 4 demonstrated significantly more growth of hair in the 2% minoxidil group than in the placebo group (p = 0.013), with no significant difference between the 3% minoxidil group and the other two treatment groups.(ABSTRACT TRUNCATED AT 250 WORDS)