This double-blind, placebo-controlled study examined the clinical efficacy and tolerance of human leukocyte interferon-alpha (2 x 10(6) IU/g) in hydrophilic cream to cure patients afflicted with first episodes of genital herpes. Sixty patients aged 18-40 years (mean 24.5) with culture-confirmed herpes simplex genitalis, bearing 755 lesions (mean 12.6) were randomized to active and placebo groups. Patients joined the study within 7 days (mean 4.1) of the manifestation of lesions. Each patient was given a precoded 40-g tube containing placebo/active preparation with instructions on self-application of the trial medication to their lesions three times daily for 5 consecutive days (max. 15 topical applications per week). Patients were examined three times a week to evaluate clinical efficacy and other beneficial effects. A reepithelialized lesion with some residual erythema was recorded as healed. Patients resolved during the active treatment period (1-4 weeks) were spared further therapy and were requested to visit us as scheduled for posttreatment control after 16 weeks. From the remaining patients empty tubes were collected, and similarly coded replacement tubes were given to continue the treatment (in total 160 tubes were used). Patients treated with leukocyte interferon-alpha cream had significantly shorter mean duration of viral shedding/healing than placebo recipients, (6.2 days vs. 15 days; P < 0.01); thus the number of healed patients was 25/30 (83.3%) vs. 5/30 (17%; P < 0.001. Of the 60 patients 49 (81.6%) complained no drug-related side effects.(ABSTRACT TRUNCATED AT 250 WORDS)