Excessive sebum production is a central aspect of the pathophysiology of acne vulgaris. Sebaceous gland function is under androgen control and it is hypothesized that dihydrotestosterone is formed by the action of 5 alpha-reductase. Type I is the controlling isoenzyme. This study describes a 3-month, multicenter, randomized, placebo-controlled clinical trial with a potent, selective inhibitor of type I 5 alpha-reductase used alone and in combination with systemic minocycline. Inhibition of type I 5 alpha-reductase was not associated with clinical improvement of acne when used alone and did not enhance the clinical benefit of systemic minocycline. These results indicate the need for further work at the molecular level to better understand the action of androgens on sebaceous gland function.