Betaseron (beta ser17-interferon) was administered to 19 patients (17 evaluable) with advanced melanoma by two schedules. Patients received either 30 X 10(6) units (mU) by intravenous bolus 5 days a week for 2 weeks followed by 2 weeks rest, or 30 mU daily for 5 days in week 1, 60 mU daily for 5 days in week 2, then twice-weekly doses escalating from 90 to 270 mU. Toxicity commonly included malaise, fatigue, fever, and weight loss. Mild hematologic, gastrointestinal, and hepatic toxicity were also seen, as well as an episode of atrial fibrillation in a patient with mitral valvular disease. No responses to therapy occurred.