Eighteen patients with advanced solid tumors were treated in a phase I study of cisplatinum in combination with recombinant alpha-2a interferon (Roferon-A, Hoffman-LaRoche, Inc, Nutley, NJ). Roferon-A was administered at a dose of 5 MU/m2 S.C. three times a week and the dose levels of cisplatinum were 15, 20, 25, 33, and 42 mg/m2/week given intravenously. All patients experienced grade I/II fatigue, nausea and vomiting. Grade III toxicity occurred in 4/6 patients at dose level 4. The dose limiting toxicities were myelosuppression [leukopenia (two patients), neutropenia (one patient), thrombocytopenia (one patient)], vomiting (one patient) and severe fatigue leading to a decrease in performance status (one patient). One patient with non-small cell lung carcinoma had a mixed response and another a minor response. The recommended dose level of this combination for phase II studies is cisplatinum 25 mg/m2/week and Roferon-A 5 MU/m2 three times a week.