A placebo-controlled trial to evaluate the efficacy and the safety of intramuscular injection of interferon-beta has been performed on 37 patients suffering from cervical intraepithelial neoplasia II (CIN II) associated with human papillomavirus (HPV) infection of the cervix: twenty-two patients were treated with interferon-beta (2 x 10(6) I.U. daily) for ten days; fifteen received placebo (2 ml of saline solution daily) for ten days. Prior to therapy, and at day 70, 190, 370, 550, 730 after the beginning of treatment, patients were examined by colposcopy and punch biopsies of the cervix. Results showed a progressive amelioration in the interferon-beta treated patients, which was statistically significant at any control station (70, 190, 370, 550, 730 days) as compared to placebo treatment. Percentages of lesions that regressed, persisted or progressed were 36.4%, 54.5%, 9.1% respectively in the Interferon-beta group, and 0%, 67.7% and 33.3% respectively in the placebo group. Interferon-beta administered intramuscularly has shown to be an efficacious treatment of CIN II (cervical intraepithelial neoplasia II) associated with HPV infection, without evident side effects; it can be used in patients requiring medical treatment with at least one-year monitoring by cervical biopsies or as an adjuvant surgical treatment (which remains the principal treatment) in the management of patients suffering from CIN II associated with HPV infection.