Eleven patients with advanced multiple myeloma (MM) received syngeneic marrow (n = 10) or peripheral blood stem cell (n = 1) transplants following cyclophosphamide (CY) and total body irradiation (TBI) (n = 8), busulfan (Bu) and CY (n = 1), Bu, CY and TBI (n = 1) or Bu, melphalan and thiotepa (n = 1). At the time of transplant one patient had stage II and 10 patients had stage III disease. Four patients had refractory disease, two had chemotherapy sensitive disease and five had progressed after an initial response to chemotherapy. The median time from diagnosis to transplant was 353 days (range 176-6118). After transplant, the median time to achieve granulocytes of 0.5 x 10(9)/l and platelets of 20 x 10(9)/l was 12 days (range 9-20) and 12 days (9-27), respectively. One patient died of interstitial pneumonia syndrome on day 32 and one died of veno-occlusive disease of the liver on day 44 post-transplant, and these were unevaluable for response. Five of nine evaluable patients achieved a complete response (CR), three a partial response, and one patient had no response. Three patients who did not achieve CR died of progressive disease 106, 142 and 321 days post-transplant. Of five patients who achieved a CR, three relapsed on days 539, 737 and 1706 and died on days 1759, 1596 and 1736, respectively; one patient died of myelodysplastic syndrome on day 1407 without evidence of MM and one patient is alive and disease-free 3297 days after transplant. One of the two long-term survivors has a persistent monoclonal protein in the blood 15 years post-transplant. These data show that high-dose therapy and infusion of normal syngeneic marrow cells can cure a small fraction of patients with MM. However, the majority of patients did not achieve durable CR, demonstrating the need for improved transplant conditioning regimens, earlier transplant or additional post-transplant treatment strategies when syngeneic transplants are performed.