Present clinical and laboratory diagnostic criteria permit a more accurate diagnosis and closer follow-up of patients with plasma cell dyscrasias. A ten-year follow-up of a group of 423 patients showed that the indications for and the adjustment of treatment are more precise when these criteria are summarized into profiles based on each diagnostic category. M components may be an indication of the presence of another sometimes nonreticular malignant neoplasm. The improvement of the specificity and sensitivity of immunologic methods sheds additional light on mechanisms controlling the synthesis of homogeneous antibodies such as prevalence of IgM-K in mixed cryoglobulinemia and lambda-light chains in IgD myeloma, excretion of lambda-Bence Jones proteins in amyloidosis, and greater IgG-subclass restriction in multiple myeloma as compared with benign monoclonal gammopathy. The activation of additional clones (biclonal gammopathies) was found in 3% of our patients.