BACKGROUND The potential role of finasteride in treating androgen related skin disorders was investigated. METHODS Pooled human dermal fibroblasts were used to assess the effect of finasteride on the 5 alpha-reductase activity in skin tissue. Vmax and Km were estimated in the presence of 0, 10, and 200 nM finasteride. RESULTS Vmax values remain constant near 1.20 pmol/mg protein/h in the presence of increasing concentrations of finasteride; however, apparent Km increases from 0.27 nM at 0 nM finasteride to 0.31 nM and 0.44 nM at 10 nM and 200 nM finasteride, respectively. This suggests that finasteride competes with testosterone and has a high affinity for same binding site of the 5 alpha-reductase enzyme. Apparent Ki was estimated at 282 nM, indicating that a high concentration of finasteride is required to significantly suppress the enzyme activity. CONCLUSIONS This study confirms that finasteride inhibits the conversion of testosterone to dihydrotestosterone in human reticular dermal fibroblasts. Finasteride may have therapeutic potential in treating skin disorders influenced by the action of dihydrotestosterone.