Acute deterioration of renal function occurred shortly after the angiotensin-converting enzyme (ACE) inhibitor, enalapril, was administered to two renal transplant patients who were also receiving cyclosporine. Renal function recovered completely in both cases upon discontinuation of enalapril. Neither patient had evidence of transplant artery stenosis or chronic rejection, conditions known to predispose to renal failure during ACE inhibitor therapy. The possibility that afferent vasoconstriction induced by cyclosporine may have predisposed these patients to renal failure from enalapril is discussed.