In an experiment on three healthy volunteers, plasma levels of tribenoside and the elimination of benzoic acid in plasma and urine were followed up during a 7-day period of daily oral medication with tribenoside. Plasma levels of tribenoside, and plasma and urine concentrations of free and total benzoic acid were determined quantitatively. The concentrations of alpha- and beta-tribenosides found in the plasma were very low and did not increase during treatment. Total benzoic acid in the plasma remained at almost the same level during treatment as that observed before treatment. Biotransformation of tribenoside therefore does not appear to result in any significant change in the plasma concentrations of free or total benzoic acid. The average daily excretion of total benzoic acid in the urine of the 3 subjects was greater during treatment than before. The average increases in total benzoic excretion in the 3 subjects correspond to 23.5, 11.9, and 23.7% of the theoretical amount that would be produced by the metabolic oxidation of the 3 benzyl groups. This study demonstrates that tribenoside does not accumulate in plasma. Around 20% of the administered dose is metabolized to benzoic acid, which is almost entirely present in the body as hippuric acid. Hippuric acid is excreted at such a rate that it does not accumulate in plasma and does not exceed the normal concentration range.