The myeloma kidney is characterized by casts in the distal and collecting tubules. The glomeruli are hardly affected unless amyloidosis is present. When the glomeruli are involved, the proteinuria is nonselective and, in some cases, the whole paraprotein is excreted in the urine. Nephrocalcinosis may be present and focal myeloma cell infiltration in the interstitium is a characteristic, but inconstant, finding. The nephrotic syndrome is extremely rare; if it exists, amyloidosis should be suspected. In contrast to multiple myeloma, the glomeruli are frequently involved in macroglobulinemia of Waldenström. Hyaline intracapillary deposits consisting of pure IgM are a characteristic finding as is infiltration of the kidney with lymphoid cells. No characteristic lesion of the kidney has been described in the heavy-chain diseases. Mixed cryoglobulinemia associated with an IgM paraprotein can produce glomerulonephritis that is due to the deposition in the glomeruli of an immune complex consisting of IgG, IgM, and complement.