Lymphoblastoid interferon, Wellferon, was used to treat patients with resistant and persistent condyloma acuminatum at initial doses of 5, 3, and 1 million unit/square meter (Mu/M2). The objectives of this study were to evaluate the efficacy and toxicity of, and tolerance to, intramuscular and intralesional interferon. Seventeen patients were treated with 5 Mu/M2, 14 patients with 1 Mu/M2, and 37 patients with 3 Mu/M2; daily administration was followed by three-times-a-week dosing. The complete response rate in patients receiving initial dose of interferon of 5 Mu/M2 was 69%, that for doses of 1 Mu/M2 was 43%, and that for doses of 3 Mu/M2 was 57%. All patients given interferon developed initial elevations of temperature of limited duration, whereas all patients given the 5 Mu/M2 dose had to have the amount reduced because of biologic side effects. However, only five of 37 (14%) of the patients given 3 Mu/M2 required a reduction in the dosage, and no patient given 1 Mu/M2 needed to have the dosage reduced. These studies suggest that interferon is efficacious in the treatment of resistant and persistent condyloma acuminatum, and that the biologic side effects were dose-related, well tolerated, and not life-threatening.