A large dose of melphalan was given to 23 patients with advanced multiple myeloma that was refractory to multiple prior treatments. Sixteen patients received a dose of 80 to 100 mg/m2, and seven were given 140 mg/m2 followed by autologous bone marrow infusion. Tumor mass was reduced by more than 75% in 14 patients, including four who died of bone marrow aplasia. Serious infections were prevented in six of seven patients who received autologous bone marrow. The marked cytoreduction in patients with previously refractory disease indicated the apparent drug resistance could be overcome by dose escalation. However, short remission times in most responding patients were consistent with rapid regrowth of primordial tumor cells with high proliferative activity. Although high-dose melphalan was of limited benefit to patients with refractory myeloma, further studies are necessary to clarify its role during earlier phases of disease.