Tritium-labeled folic acid was given intravenously to normal male volunteers and the nature of the folate compounds appearing in the urine was studied by column chromatography and microbiologic assay.

Three peaks of activity were obtained and these were due to (a) N10-formyl folate and p-amino-benzoylglutamate, (b) N 5-methyl-tetrahydrofolate, and (c) pteroylglutamic acid. Peaks (a) and (c) were tritium-labeled, but peak (b), containing 5-methyl-tetrahydrofolate, was not tritium-labeled.

It was concluded that between one-quarter to one-third of the folic acid activity in urine following a small parenteral dose was due to 5-methyltetrahydrofolate, but that this arose by displacement from the tissue (presumably liver) and not from the administered dose of folic acid.

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