A double-blind, placebo-controlled study was done to evaluate the efficacy of an alpha interferon preparation in 128 patients with recurrent genital herpes. The preparation containing 10(5) or 10(7) U alpha interferon with nonoxynol 9 in a cream base (Exovir-HZ) was applied three times daily for 5 days. The treatment did not cause any adverse reactions. Patients treated with either interferon concentration became negative for viral culture at a faster rate than placebo recipients. The end of new lesion formation, scabbing, and the healing of lesions were all superior in patients treated with 10(5) U to those treated with 10(7) U interferon. End of new lesion formation and scabbing were also statistically different in patients treated with 10(7) U from those patients treated with placebo. Results suggest that topical interferon might be useful in relieving symptoms of severe cases of genital herpes.