Topical minoxidil is a trichogenic agent that stimulates the hair follicle via the vasoactive metabolite minoxidil sulfate without any evidence of antiandrogen activity or an effect on the immune system. Less than 5% of the applied dose is absorbed. The therapeutic effect on hair regrowth is demonstrated for androgenetic alopecia in males and females, by a computer-assisted image analysis counting technique of nonvellus hairs from a photographic print. Patients with severe alopecia areata respond poorly to topical minoxidil treatment. The most common adverse reactions are limited to irritant and allergic contact dermatitis on the scalp. The use of retinoic acid with topical minoxidil has been disappointing relative to the increase in systemic exposure. The value of topical minoxidil as an adjunct for the hair transplant procedure and its effect on hair loss from chemotherapy are being evaluated.