Indoramin hydrochloride is a new alpha 1-adrenoceptor antagonist. Eleven hypertensive men in whom the BP was normalized with indoramin underwent assessment of renal function, renal hemodynamics, and body fluid composition following short-term (three to six weeks), long-term (five to six months), and withdrawal (two weeks) therapy. Short-term indoramin therapy produced a 28% increase in glomerular filtration rate, a 24% increase in effective renal plasma flow, and a 31% decrease in renal vascular resistance. Although urine flow rate and free water clearance were unchanged, fractional sodium excretion decreased 38%. Long-term indoramin therapy was associated with qualitatively similar renal effects, but the changes did not achieve statistical significance. Plasma volume was increased only during short-term therapy; however, body weight was increased following both short- and long-term therapy. Indoramin effectively lowers BP without producing deleterious renal effects.