Ascites is an unusual feature of multiple myeloma. We report a case of ascites occurring early in the course of a patient with myeloma in whom there was no evidence of intra-abdominal plasmacytoma, and the skeleton was relatively spared. The serum contained predominantly polymeric IgA, a feature not investigated in previous cases. We reviewed the relevant literature and will discuss the suggestion that human myelomas presenting with the triad of ascites, relative or absolute sparing of the skeleton, and an IgA paraprotein bear an analogy to mouse myelomas induced by intraperitoneal instillation of irritants. The relevance of polymeric IgA is discussed with respect to tissue origin of the paraprotein. Seventeen cases were identified consistent with a definition of "myelomatous ascites" (malignant myeloma in which plasma cells and/or monoclonal immunoglobulin can be demonstrated in ascitic fluid). IgA immunoglobulin class was present at three times the incidence seen in myelomas in general (five of seven cases were specified). In twelve patients there was no identifiable intra-abdominal plasmacytoma although liver infiltration was common. Amyloidosis was reported in only one case, and no cases of uncomplicated plasma cell leukemia were noted. Ascites was a presenting feature in five cases. In each of these five there was absolute or relative sparing of the skeleton, four had no evidence of plasmacytoma, and the paraprotein was IgA in three, IgG in one, and unreported in one. In no case was there a known history of chronic intra-abdominal irritation.