The purpose of this study was to evaluate a new regimen for the treatment of multiple myeloma based on alternating 3-week cycles of chemotherapy and interferon (rIFN alpha 2). In this prospective phase II clinical trial the Eastern Cooperative Oncology Group evaluated a regimen consisting of 2 cycles of VBMCP (Vincristine 1.2 mg/M(2) IV d1, BCNU 20 mg/M(2) IV d1, Melphalan 8 mg/M(2) PO dl-4, Cyclophosphamide 400 mg/M2 IV d1, Prednisone 40 mg/M(2) PO d1-7) followed by alternating 3-week cycles of VBMCP and rIFN alpha2 5 Mu/M(2) SC 3x/week. Treatment was administered for 2 years. Fifty-eight patients with previously untreated multiple myeloma were entered. Objective response (OR) required 50% decrease in M-protein with correction of severe anemia and no progression of skeletal disease. Complete remission (CR) was defined by disappearance of M-protein and normalization of the bone marrow morphology. Life table analysis was utilized to express survival and response duration. Fifty-four patients were evaluable. Objective response was seen in 80% of patients including CR in 30% (16 patients). The median response duration is 35 months, 46 months for patients with CR. The median survival is 42 months for all patients. Five year survival is 42%. Although 78% of patients had neutrophil nadirs <1000 x 10(9)/L, the incidence of severe infection was only 9%. These data demonstrate that VBMCP + interferon is an effective new regimen combining chemotherapy with a biological response modifier for the treatment of multiple myeloma. The incidence of CR is high, and the response and survival durations appear to be 1 year longer than usually seen with standard chemotherapy. A current ECOG randomized trial compares VBMCP + interferon with VBMCP alone.