Clinical and electrophoretic data were evaluated in 334 consecutive patients with myeloma or monoclonal peaks on serum or urine electrophoresis. Of the 242 patients with myeloma, 7% had localized plasmacytomas with absent or low level monoclonal peaks on electrophoresis and received only radiotherapy to focal disease areas. Chemotherapy was also withheld from eight other patients in an indolent clinical phase of multiple myeloma. Disease progression was apparent in about one third of the patients with localized and indolent myeloma within 12 months. Forty-three patients had idiopathic peaks on serum electrophoresis; more than 90% were of the IgG type with levels less than 3.0 gm/100 ml. Serial electrophoreses, immunoglobulin quantitations, and skeletal radiographs are recommended for the evaluation of patients with idiopathic peaks, the classification of early phases of myeloma, and the confirmation of tumor mass change.