Following administration of a single dose of [U14C]cyanidanol-3 to human volunteers, a mean of 55% of the dose of 14C was excreted in urine; 90% of urine 14C was excreted within 24 h of drug administration. The major urinary metabolites were the glucuronides of (+)-catechin and 3'-O-methyl-(+)-catechin, and the sulphate of the latter. These three conjugates collectively accounted for three quarters of urine 14C. Urinary excretion of unchanged (+)-cyanidanol-3 was 0.1-1.4% dose. (+)-Cyanidanol-3 and metabolites containing the intact flavanol ring system accounted for 90% of urine 14C. Ring scission was, under these conditions, a minor metabolic pathway resulting in the excretion of small amounts of 3-hydroxybenzoic acid, 3-hydroxyhippuric acid and 3-hydroxyphenylpropionic acid. Unchanged (+)-cyanidanol-3 was detected in plasma between 30 min and 12 h after administration. Metabolites (as total 14C) persisted in plasma for at least 120 h after administration.