A diagnosis of nonsecretory myeloma was established in two patients with anemia and proteinuria on the basis of the suppression of polyclonal immunoglobulins and the increase of plasma cells in the bone marrow. No paraprotein was detected in the serum or concentrated urine of these patients. However, a plaque-forming assay of bone marrow cells showed the secretion of monoclonal immunoglobulin by the myeloma cells. Moreover, renal biopsies from both patients indicated the deposition of monoclonal light chains in the glomerular mesangium and basement membrane, as well as in the tubular basement membrane, a pattern consistent with light-chain deposition disease. These observations suggested that the secreted paraprotein disappeared rapidly as a result of enhanced catabolism or deposition in organs such as the kidney, producing severe proteinuria and chronic renal failure. The plaque-forming assay is a useful technique for the demonstration of this type of nonsecretory myeloma, pseudo-nonsecretory myeloma.