Effects of antihypertensive treatment on renal function were analyzed in data from a prospective, double-blind investigation of 840 patients randomly assigned to placebo or to active treatment with a combination of triamterene and hydrochlorothiazide. Baseline serum creatinine levels were significantly and positively correlated to age, gender (higher in men), systolic blood pressure, and history of cardiovascular complications. During a five-year follow-up period, serum creatinine levels increased significantly in treated patients but not in placebo patients. Five patients died of renal causes (one in the placebo group, four in the treated group), and five patients dropped out of the study because of an increase in serum creatinine of more than 100% (four received active treatment). The incidence of renal complications in the hypertensive elderly is small. The current data do not support the hypothesis that renal deterioration can be prevented by antihypertensive treatment.