Between 1990 and 1997, 55 patients with high risk multiple myeloma underwent high-dose therapy with peripheral blood stem cell transplantation. Intensification consisted of high-dose L-PAM in 54 patients, and 15 patients underwent a second high-dose treatment. Thirty patients received total body irradiation. Twenty patients were more than 60 years old. Thirty-five patients were intensified during first response. The overall response rate was 78%. There were four toxic deaths. The median overall survivals after intensification and after first treatment of myeloma were greater than 48 months and 71 months, respectively. Conversely freedom from progression after intensification was short, with a median of 22 months. Freedom from progression was significantly shorter in patients older than 60 (12 months), and in patients who had received more than 75 mg/m2 of L-PAM before intensification (16 months). Although intensification is feasible in elderly patients the benefit appears to be reduced in this subgroup of patients. Prior therapy with high cumulative doses of L-PAM should be avoided in patients who will receive high-dose L-PAM for therapeutic intensification.