The pharmacokinetics of bethanidine‐14C was studied in three hypertensive patients. A 25‐mg dose of bethanidine‐14C hemisulfate was administered intravenously. Plasma levels of drug were measured over the first 6 hr. In 3 to 4 days, 89% to 94% of the dose was excreted in the urine. Thin‐layer chromatography (TLC) and isotope dilution analysis of the urine samples indicated that only intact bethanidine was excreted. Plasma level and urinary excretion rate profiles had multiphasic characteristics. Estimated half‐lives of the terminal phase ranged from 7 to 11 hr. A verage renal clearance over the initial 6 hr approached renal plasmafiow. In 2 of the patients, renal clearance between 2 and 4 hr after administration was reduced to one‐half that observed during the initial 2‐hr period. After single oral administration of a 25‐mg dose of bethanidine‐14C hemisulfate, 48% to 61% was excreted in urine and 15% to 48% infeces. Peak urinary excretion rates were reached 6 hr following administration. The urinary excretion kinetics of bethanidine during and after repetitive oral dosing was also studied. A 25‐mg dose was divided into 12 to 16 equal doses and administered every 6 hr. A larger fraction of the cumulative dose was recovered in the urine (72% to 74%) than after the single dose, suggesting higher availability at the lower dose. Steady‐state urinary excretion rates were achieved in 4 to 7 doses. The steady‐state urinary excretion levels were consistent with pharmacokinetic predictions based on single oral dose data. When 2 of the patients were given imipramine for 2 days prior to an oral 25‐mg dose of bethanidine‐14C hemisulfate, the terminal half‐lives of the urinary excretion rate profiles were shorter than those in the same patients not given imipramine.