OBJECTIVES: I. Compare the efficacy of melphalan with or without holmium Ho 166 DOTMP followed by autologous peripheral blood stem cell transplantation in patients with multiple myeloma. II. Compare the response rate and overall survival of these patients treated with these regimens. III. Compare the hematologic recovery rate and time to granulocyte engraftment of these patients treated with these regimens. IV. Compare the toxicity of these regimens in this patient population.