Pharmacokinetics of tritium-labeled exaprolol, 1-(2-cyclohexyl[2,4-3H]-3-isopropylamino-2-propanol, a potent beta-adrenergic blocker, was studied in rats. The assay of the parent drug in plasma and excreta was based on extraction into toluene and TLC. In rats elimination half-lives of exaprolol after iv and oral administration of 26.8 and 40.1 hr, respectively, were found; the bioavailability was 26.7%. After oral administration to rats, the drug was rapidly and completely absorbed. The long retention of exaprolol in tissues of iv injected rats was reflected by the steady-state distribution volume of 59.38 liters/kg and the clearance rate of 1.44 liters/hr/kg. The total 3H excreted in urine within 96 hr after iv or oral administration to rats amounted to 47.9 and 47.1% of dose, respectively, and in feces to 34.2 and 29.8%, respectively. The ratio of 3H-exaprolol to total 3H concentration in plasma, urine, and feces of rats indicated a moderately extensive metabolism of the parent drug. The substance was about 50% bound to human serum albumin. The rat erythrocyte/plasma partition coefficient rose with exaprolol concentration.