Topical 5% minoxidil solution was used to treat 47 patients with severe alopecia areata. Forty patients (85%) had terminal hair regrowth after 48 to 60 weeks of treatment. In the majority of patients, hair regrowth was not cosmetically acceptable. Data were compared with those from a previous study with topical 1% minoxidil solution. Both the percentage of responders and the quality of their hair regrowth were significantly greater with 5% than with 1% topical minoxidil solution. One patient developed an allergic contact dermatitis to minoxidil, but no systemic side effects were detected. The results strongly suggest a dose-response effect for topical minoxidil treatment of alopecia areata and the importance of exploring modifications in dosing and delivery systems to enhance therapeutic efficacy.