Latanoprost, a selective FP prostanoid receptor agonist used in the treatment of glaucoma, has a hypertrichotic side effect. Using the macaque model of androgenetic alopecia, we examined the effect of latanoprost on hair growth. Eight monkeys were divided into 2 groups; one group received a daily topical application of 50 microg/ml of latanoprost for 5 months; a control group had a daily application of vehicle. For an additional 3 months, 2 monkeys from each group were given 500 microg/ml latanoprost, while the remaining monkeys continued with the previous treatment. Hair growth was evaluated by monthly photographs and phototricho-graphic analysis. Fifty microg/ml of latanoprost caused minimal hair growth. Latanoprost at 500 microg/ml induced moderate to marked hair regrowth with 5-10% conversion of vellus hairs to intermediary or terminal hairs. The vehicle group showed no effect. Further evaluation of latanoprost as an agent for treatment of human androgenetic alopecia is indicated.