A high remission rate is achieved with high-dose melphalan (HDM) in multiple myeloma (MM), and autologous transplantation of hematopoietic stem cells allows a prompt hematologic recovery after high-dose therapy. We treated 97 patients with high-risk MM (group 1:44 advanced MM including 14 primary resistances and 30 relapses; group 2: 53 newly diagnosed MM) with a first course of HDM. For responding patients a second course of high-dose therapy with hematopoietic stem cell support was proposed. After the first HDM, the overall response and complete remission rates were 71% and 25% with no significant difference between the two groups. The median durations of neutropenia and thrombocytopenia were significantly longer in group 1 (29.5 days and 32 days, respectively) than in group 2 (23 days and 17 days, respectively). This severe myelosuppression led to eight toxic deaths and the fact that only 38 of the 69 responders could proceed to the second course (three allogenic and 35 autologous transplantations). Among the 35 patients undergoing autologous transplantation (10 in group 1, 25 in group 2), 31 received their marrow unpurged collected after the first HDM, and four received peripheral blood stem cells. The median durations of neutropenia and thrombocytopenia after autologous transplantation were 24 days and 49 days, respectively. Two toxic deaths and nine prolonged thrombocytopenias were observed. The median survival for the 97 patients was 24 months (17 months in group 1, 37 months in group 2) and the median duration of response was 20 months. The only parameters that have a significant impact on the survival are the age (+/- 50 years) and the response to HDM. The median survival of the 35 patients undergoing autologous transplantation is 41 months, but the median duration of remission is 28 months with no plateau of the remission duration curve. Patients responding to HDM may have prolonged survival, but even a second course of high-dose therapy probably cannot eradicate the malignant clone.