Thirty patients with disseminated malignant melanoma received intramuscular recombinant leukocyte A interferon (rIFN-alpha A), 12 X 10(6) U/m2, three times weekly for a planned treatment duration of three months. This dose was selected in view of our prior phase II data indicating that 50 X 10(6) U/m2 three times weekly produced excessive toxicity. In this current trial we observed three objective partial regressions (20%) among the 15 better-risk patients (performance score 0, 1, and no prior chemotherapy) with times to disease progression of 1.9, 9.6, and 12.9+ months. There were also three regressions (one complete and two partial) among the 15 poor-risk patients (performance score 2, 3, or prior chemotherapy) with progression times of 3, 3.2, and 9.6+ months. For all patients, the median survival time was 4.2 months. One half of the patients were observed to have progressive disease within one month of commencing treatment. Responding metastatic lesions were limited to soft tissue, although one patient also had a partial response of a lung nodule. The most substantial toxicities were moderate-to-severe myalgias (27%), nausea (33%), anorexia (47%), and fatigue (50%). Among the 22 patients with weight loss, the median was 2.3 kg (range, 0.6 to 8.4 kg). Hematologic and hepatic toxicity was transient and of little clinical significance. Our study indicates that rIFN-alpha A in the dose and schedule that we used is clinically tolerable and has antitumor activity in malignant melanoma. The response rate was similar to results observed in our previous study of a higher dose regimen.