Fourteen patients with chronic genital warts were entered in a pair-matched crossover trial of recombinant interferon-alpha-2a. They received daily doses of either 1.5 X 10(6) U or 18 X 10(6) U interferon for one week by the subcutaneous route (abdominal skin). After an observation period of 4 weeks in case of no change or partial response, patients of the low-dose group were given 18 X 10(6) U and those of the high-dose group 3 X 10(6) U daily for another 7 days. Eight of 14 patients had a complete remission by the end of the therapy-free interval of 4 weeks, 5 patients of the low-dose group and 3 patients of the high-dose group. Acute side-effects consisted of a transient influenza-like syndrome. Remissions have been maintained for 6 to over 10 months. The data implicate that recombinant interferon-alpha-2a is highly effective in patients with human papillomavirus-related genital warts and that the low-dose regimen is at least equivalent to the high-dose treatment.