The ability of triamterene to control blood pressure, alter the renin-aldosterone axis and cause clinical and biochemical side effects was assessed. In addition, because of the many undesirable side effects of spironolactone, triamterene was evaluated as a suitable alternative potassium-sparing diuretic in the treatment of hypertension. Triamterene was not an effective antihypertensive agent despite presumed volume depletion in patients as reflected by an increase in plasma renin activity and aldosterone excretion rate. There was also a significant but reversible deterioration in renal function in 20 patients treated with triamterene as the dose was increased. BIBLIOGRAPHIC REFERENCE: Mitchell, J.R., A.A. Taylor, C.R. Lake, D.E. Rollins and F.C. Bartter: NIH Combined Clinical Staff Conference: Renin-aldosterone profiling in hypertension. Ann. Intern. Med. 1977 (In press).