Renal function was studied before and after percutaneous transluminal renal angioplasty (PTRA) in 79 patients. In a prospective study of 28 patients with unilateral renal artery stenosis, renal function was similar during angiotensin-converting enzyme (ACE) inhibition and after PTRA. In 37 patients with bilateral renal artery stenoses, 9 patients with solitary kidneys and renal artery stenoses and 5 patients with transplant renal artery stenoses, there was no statistical difference in the renal function before and after PTRA. Of the 79 patients studied, 50 had normal renal function before PTRA. In 5 of these renal function decreased, requiring temporary hemodialysis in 1. Of 29 patients with impairment of renal function due to renal artery stenosis, improvement was noted in 14, stabilization of renal function in 11, and decrease of renal function in 4. It is concluded that PTRA is a safe technique that can make life-long drug treatment unnecessary in antihypertensive patients. It can restore or stabilize renal function in renal insufficiency caused by renal artery stenosis. It has to be kept in mind that contrast medium toxicity and cholesterol embolization can induce severe renal insufficiency after PTRA.