The urinary excretion of total 14C after oral administration of 25 mg (approximately 1 mumol/kg) 14C-felodipine to man, and intragastric administration (5 mumol/kg) to dog, rat and mouse, was 70, 39, 44 and 53% dose, respectively, in 72 h. Metabolites of felodipine were separated and quantified by h.p.l.c. Unchanged felodipine and its oxidized analogue were not excreted by any of the species studies. Three metabolites, present in all species studied, were isolated from urine and identified as products of the oxidation of felodipine to its pyridine analogue followed by hydrolysis of one or both of the pyridine carboxylic acid esters.