1 The synthesis of [14C]-debrisoquine hydrochloride and 4-hydroxy-debrisoquine sulphate is described. 2 The metabolic fate and excretion profile in both urine and faeces of 14C-labelled debrisoquine was studied in five healthy human subjects. 3 Investigations showed that the drug is well-absorbed after a single oral dose of 32 mg and quantitatively eliminated from the body within three days. 4 4-Hydroxy-debrisoquine is the major metabolite of debrisoquine, although significant amounts of 5-,6-, 7- and 8-hydroxy-debrisoquine are also formed. 5 Electron-capture gas chromatography is a useful method for measuring debrisoquine and its five hydroxylated metabolites in urine at the pg level.