Interferon alfa-2b (Intron A; Schering Plough) has been shown to be active in advanced previously treated multiple myeloma (MM). Recent in vitro evidence has suggested synergy between cytotoxic agents and interferon alfa-2b. This phase I-II protocol was initiated to study interferon alfa-2b in combination with melphalan and prednisone. Groups of five patients received interferon alfa-2b twice-weekly for two weeks at dose levels of 0.5, 1.0, 2.0, 5.0 and 10.0 X 10(6) IU/m2. During week 2, melphalan (9 mg/m2) and prednisone (40 mg/m2) were administered concurrently with interferon alfa-2b followed by a rest period during nadir myelosuppression, the cycles being repeated every 28 days. Thirty patients were entered of whom 21 were Stage III, 3 Stage II and 6 Stage I. Median nadir WBC/mm3 and platelets/mm3 at the various dose levels are given in the table. Serious adverse reactions while on study included myocardial infarction, renal failure and leukopenia-related sepsis. Early response information is available. Twenty-six patients are evaluable for response. Seven have had progressive disease and 19 (69%) a partial response, the median duration was 11+ months. Interferon alfa-2b does not appear to antagonize melphalan/prednisone effectiveness and may be additive or synergistic. Full evaluation of this combination will be undertaken in randomized controlled trials which are now underway.