Since 1986, we have treated young patients with aggressive multiple myeloma (MM) by high-dose chemotherapy (HDC) and total body irradiation (TBI) followed with autologous blood stem cell transplantation (ABSCT). To evaluate this strategy: 1) We conducted a phase II trial that included 63 patients. Within a median follow-up of five years after transplantation, overall survival was 60% and median event-free survival was four years, and 2) In the early 1990s, we initiated a prospective trial where, after collection of chemotherapy-mobilized ABSC, patients under 55 years of age with newly diagnosed MM were randomly assigned either to HDC and TBI supported with ABSCT (high-dose therapy [HDT] arm) or to a conventional vincristine, melphalan, cyclophosphamide and prednisone (VMCP) regimen (VMCP arm). In the latter, HDT with ABSCT was performed as a rescue therapy, in case of primary resistance to VMCP or at relapse in responders. As of June 1994, 167 patients have been enrolled since a median time of 26 months. Fourteen (8%) could not be randomized. Among the randomized patients (n = 153), 30 deaths were observed, 13 in the HDT group and 17 in the VMCP group (p = 0.28, two-sided log rank test). Overall survival rates at two years were estimated at 78% for all 167 patients, at 82% in the HDT group and at 67% in the VMCP group. ABSC, provided they are collected early in the disease course, allow a great majority of myeloma patients to receive HDT.(ABSTRACT TRUNCATED AT 250 WORDS)