1. The metabolic fate of N,N-dimethylcarbamoylmethyl 4-(4-guanidino[¹⁴C]benzoyloxy)phenylacetate methanesulphonate (¹⁴C-camostat mesylate) was investigated after i.v. administration to man (12-h infusion), and to rat and dog (bolus injection).

2. Renal excretion (mainly in 24 h) accounted for at least 80% dose in all three species, and the only two important metabolites were identified as 4-(4-guanidinobenzoyloxy)phenylacetic acid (GBPA) and 4-guanidinobenzoic acid (GBA).

3. Parent drug was not detected in human plasma either during or after infusion of ¹⁴C-camostat mesylate owing to rapid hydrolysis of the side-chain ester group (t_1/2 < 1 min). Steady-state levels of both GBPA and GBA in plasma were apparently attained by the end of the infusion period. Mean terminal half-life, systemic clearance and apparent volume of distribution at steady-state of GBPA in man were 1·0 h. 6·4 ml/min per kg and 0·381/kg, respectively, and the corresponding values for GBA were 2·4 h, 4·7 ml/min per kg and 1·01/kg respectively.

4. Radioactivity was rapidly distributed to most tissues after bolus i.v. doses of ¹⁴C-camostat mesylate to rats and dogs, with highest levels being associated with the liver and kidney, the two main organs of drug elimination. Concentrations in the pancreas, a possible site for drug action, were generally lower than those in plasma.