Therapeutic drugs are well-recognized as a cause of the nephrotic syndrome in humans. However, documentation of the renal histopathologic features is lacking or incomplete in many cases. Even when accurate histopathologic information is available, there is little evidence to support a specific pathogenetic mechanism of renal injury in the vast majority of cases. We describe a patient with diabetes who had hepatitis and dermatitis in association with the use of chlorpropamide. In addition to these well-described toxic reactions to this drug, the nephrotic syndrome developed. Renal biopsy revealed the presence of a proliferative glomerulonephritis that was shown to be of an immune complex nature on immunofluorescence and electronmicroscopic study. Serial serum complement levels and circulating immune complex levels were consistent with an immunologically mediated reaction. Repeated renal biopsy documented resolution of the renal changes. Thus, in this patient, a drug-induced nephrotic syndrome was associated with a proliferative glomerulonephritis, probably due to the formation of immune complexes.