Our previous study of senile skin showed the capacity of topical, but not systemic, testosterone propionate to stimulate hair growth in the axilla and on the forearm. As an extension of this finding, androgen creams were applied to the scalps of 21 bald men. Approximately 75% of the group showed some stimulation of hair growth, as indicated by longer, thicker, more pigmented hairs in the bald area. Within five months of treatment approximately 10% to 15% of the follicles were stimulated to produce terminal type hairs. The probability of regrowth is dependent neither on the duration of the baldness nor on the age of the subject. The enhanced growth is not thought to be an expression of the hormonal activity of testosterone, which in predisposed subjects is a prerequisite for common baldness, but rather a pharmacological local effect on the synthetic activities of the underlying connective tissue. These results indicate the possibility of effective prophylaxis against common baldness; however, indiscriminate use of topical testosterone for its treatment, at this stage, is unjustifiable.