Human leukocyte interferon (HLI) was used in a randomized study of patients with precancerous states on the uterine cervix. The daily dose of HLI was 10(6) units and its was applied by the contraceptive pessary technique. In patients how had had only viral alterations on the cervix the treatment lasted 14 days (Singer et al. 1979) and in those with changed cytologic findings 21 days. The cytologic findings of the interferon treated patients showed no progression of the pathologic process during the ensuing 2 years. In the control group, however, they showed the aggravation of the process and the patients were directed to surgical therapy. The control of cytologic findings has been continued and in now performed at 3 month intervals.