We evaluated blood concentrations of bcl-2, a proto-oncogene that can inhibit apoptotic phenomena, in a group of patients with immunoglobulin A (IgA) nephropathy. Concentrations of bcl-2 were higher in patients with proteinuria than in those without proteinuria. A 6-month course of 5 mg/day lisinopril given to subjects with proteinuria significantly reduced blood bcl-2 concentrations and caused a reduction in proteinuria. Therefore increased blood bcl-2 concentrations may be considered an index of risk in subjects with IgA nephropathy, and the positive effects of angiotensin-converting enzyme inhibitors on proteinuria in patients with IgA nephropathy may be attributed, at least in part, to their effect on the mechanisms that regulate apoptosis. This is of fundamental importance in resolving glomerular hypercellularity in the course of glomerulonephritis.