The absorption, metabolism and excretion of ketanserin [+)-3-[2-[4-(4-fluorobenzoyl)-1-piperidinyl]ethyl]-2,4(1H,3H)- quinazolinedione, R 41 468), a novel serotonin S2-receptor antagonist used in hypertension, was studied after a single oral dose of 14C-ketanserin tartrate in three healthy subjects. Absorption from the gastrointestinal tract was rapid and almost complete. The excretion of radioactivity amounted to about 90% after 4 days and was more abundant in urine (68%) than in faeces (24%). Ketone reduction and oxidative N-dealkylation at the piperidine nitrogen were by far the two main metabolic pathways. The former pathway resulted in ketanserin-ol, the main metabolite in plasma as well as in urine (24% of dose) and faeces (5%), the latter pathway in the urinary metabolite 1,4-dihydro-2,4-dioxo-3(2H)quinazolineacetic acid (20%). Other pathways were aromatic hydroxylation at the quinazolinedione moiety and the formation of ether glucuronides. None of the metabolites substantially contributes to the overall pharmacological activity of ketanserin. The metabolic pathways of ketanserin in man were identical to those revealed previously in rats and dogs, but the mass balance of the major metabolites resembled more that in dogs than that in rats.