Twelve patients with advanced condylomata acuminata were treated by systemic human leukocyte interferon (IFN) therapy. Semi-purified and purified preparations were both able to affect condylomatous growth. Treatment of the patients at various periods of their disease resulted in one complete remission, 6 partial remissions, 4 minimal responses while one case showed progressive disease. Side-effects were unexpectedly common in these advanced patients and 4 of them had to stop IFN treatment.