Abstract1. The synthesis of [14C]pindolol labelled in the isopropyl group of the sidechain is described.2. Nine metabolites of pindolol have been separated from the urine of rhesus monkeys, rats, cats and rabbits.3. Pindolol is metabolized along four different pathways: (a) Side-chain conjugation with glucuronic acid (metabolites Ia and Ib); (b) hydroxylation or oxidation and conjugation of the indole ring, giving the indolin-2-one analogue of pindolol (IV), 3-hydroxy-pindolol sulphate (V), 5-hydroxy-pindolol glucuronide (II) and sulphate (VI), 6-hydroxy-pindolol glucuronide (III) and the side-chain glucuronide of the indigotin like derivative of pindolol (VIII); (c) oxidative ring scission to the corresponding anthranilic acid derivative (VII); (d) side-chain oxidation and deamination to 3-(5-indolyloxy)lactic acid (IX).