Percutaneous angioplasty of the renal artery was performed in 79 patients who had stable or climbing serum creatinine levels greater than 1.7 mg/dl and hemodynamically significant stenosis of the renal artery. Patients who had nonrenal causes of azotemia, nephropathy caused by iodinated contrast material, or serum creatinine levels that were declining while the patients were receiving medical therapy before angioplasty were excluded from the study. Angioplasty resulted in a significant (greater than 20%) decline in the level of serum creatinine (average, 2.7 mg/dl before to 1.7 mg/dl after) in 43% of these patients during an average follow-up period of 16 months. A significant decrease in the level of serum creatinine was seen in 61% of patients with bilateral stenosis, 38% of patients with unilateral stenosis with absent contralateral renal blood flow, and 38% of patients with unilateral stenosis and normal contralateral renal blood flow. Recapture of lost nephron function was least successful in patients whose levels of serum creatinine were greater than 4.0 mg/dl (14%); this included one (11%) of nine patients who were already on hemodialysis. We conclude that angioplasty of the renal artery can play a major role in the treatment of patients who have mild azotemia and bilateral stenosis of the renal artery. It is less successful in treatment of patients who have severe azotemia and those who have unilateral disease.