We studied 29 patients affected by acute renal failure due to multiple myeloma with Bence-Jones proteinuria greater than 1 g/day to evaluate the effectiveness of plasma exchange in the treatment of severe myeloma nephropathy. Renal failure was severe enough to require dialysis in 24 cases, while the remaining 5 patients showed serum creatinine levels greater than 5 mg/dl. The patients were randomly allocated to Group I (15 patients undergoing plasma exchange together with corticosteroids, cytotoxic drug, hemodialysis only when needed) or to Group II (14 patients undergoing peritoneal dialysis together with corticosteroids and cytotoxic drug). In Group I Bence-Jones proteinuria decreased dramatically (P less than 0.01) with a significant increase in urine output (P less than 0.001), while Group II presented a slight reduction in Bence-Jones proteinuria without a significant increase in daily diuresis. Thirteen out the 15 Group I patients recovered renal function reaching serum creatinine levels less than or equal to 2.5 mg/dl in most cases. Only two patients in Group II improved renal failure well enough to stop dialysis. The one-year survival rate was significantly higher in Group I (66%) than in Group II (28%, P less than 0.01). We conclude that plasma exchange associated to chemotherapy rapidly removes large amounts of light chains, improves both renal function and long-term survival expectancies.