The blood levels of 14C, emanating from 14C-acetyl-salicylic acid (14C-ASA) p.o. and 14C-salicylic acid i.v., were decreased and unchanged, respectively, by the concomitant oral ingestion of phenacetin. Subsequent investigation showed that phenacetin: (a) did not affect the total renal excretion of 14C or ASA metabolites; (b) enhanced the retention of 14C, from either 14C-ASA or 14C-phenacetin, in the stomach contents and stomach tissues; (c) delayed stomach emptying, and (d) did not form undialyzable or insoluble complexes with ASA. It was concluded that phenacetin reduced the blood levels of salicylate by inhibiting stomach emptying.