Bethanidine was administered intravenously to six hypertensive patients with normal renal function and five hypertensive patients with renal impairment. After administration of 0.7 mumole/kg, blood was sampled at frequent intervals for measurement of plasma bethanidine. The plasma levels were analyzed on a three-compartment exponential open-model system. The second rapid elimination phase (beta) had a half-time of 3.4 hours in normal subjects and was insignificantly prolonged to 16.4 hours in renal impairment. There was an extended terminal elimination phase of 90 and 70 hours for normals and impaired, respectfully. The volume of distribution at pseudoequilibrium was 2.8 and 1.6 liters/kg, respectively, suggesting significant sequestration of the drug in body tissues. The pharmacokinetic constants of bethanidine in normal and impaired renal functions were similar.