Efficacy of interferons on bowenoid papulosis and other precancerous lesions. Preliminary results of an open randomized trial of recombinant interferon gamma in patients suffering from bowenoid papulosis are described. Recombinant interferon gamma was given subcutaneously to 12 patients at a daily dose of 4 X 10(6) I.U. by injection. Four patients each were assigned to one of three treatment groups consisting of continuous therapy (group A) with three subcutaneous injections per week for 13 weeks; intermittent block therapy (group B) with four six-week cycles consisting of five injections on days 1, 3, 5, 7, and 9 of each cycle; and intermittent single-dose therapy (group C) with six four-week cycles consisting of only one subcutaneous injection on day one of each cycle. At the twenty-sixth week after onset of therapy, complete responses were seen in three of four patients of treatment group A, whereas in the treatment groups B and C only one patient, respectively, responded partially. These results suggest that in contrast to condylomata acuminata bowenoid papulosis lesions respond better to continuous than to intermittent interferon gamma injections. 