Three patients treated with intravenous immunoglobulin developed respiratory difficulty and decreased renal function. Previously reported adverse reactions to this class of drugs have included pulmonary toxicity but not, to the best of our knowledge, renal toxicity. Renal dysfunction was mild in one patient but severe in two patients, one of whom required temporary hemodialysis. In all three patients, renal function returned to the pretreatment level after stopping the drug. Urinalysis and urine sodium concentration at the onset of renal failure were consistent with pre renal azotemia although renal biopsy performed later in one patient showed acute tubular necrosis. The exact mechanism of toxicity is unknown, but the fact that all three cases occurred with a particular immunoglobulin preparation would suggest that a contaminant, possibly aggregated IgG might be responsible.