Ninety patients with alopecia areata were treated with weekly applications to one side of the head of dinitrochlorobenzene (DNCB) dissolved in acetone, the other side of the head serving as control region. In 80 patients (89%) hair regrew either exclusively on the treated side, or considerably faster and denser on this side. The difference was noted, in the majority of cases, within eight weeks. The initial response, however, could not be maintained in all of these patients. Persistent response was observed in 72 patients (80%). Peribulbar round cell infiltrates were found to be more constant and denser on the treated side, suggesting that topically applied DNCB affects the peribulbar infiltrate present in alopecia areata. Possibly, the therapeutic result is due to altered local immunoregulation.