Some observations on the urinary excretion of glycine conjugates by laboratory animals.

1. An isotope dilution assay has been developed for measuring the amount of conjugated glycine present in urine. The average daily excretion of conjugated glycine by male and female mouse, rat, guinea-pig and rabbit has been determined. 2. The glycine conjugates excreted by the four species have been identified. All species excreted only benzoylglycine and phenylacetylglycine. 3. The metabolism of [carboxy-14C]benzoic acid and [1-14C]phenylacetic acid has been investigated in the Sprague-Dawley rat. When administered over a range of concn. from 10 microgram/kg to 1g/kg, benzoic acid is converted to hippuric acid while phenylacetic acid is converted to phenylacetylglycine and phenylacetylglutamine. 4. Neither the rate of excretion nor the composition of the urinary metabolites arising from each acid is changed when low doses of one acid are co-administered with a high dose of the other. 5. The origin of the conjugated benzoic and phenylacetic acids is discussed.