1. A number of folates labelles with 14-C were administered orally to rats, at various doses, and urinary, faecal and hepatic folates examined. 2. 10-Formylpteroylmonoglutamic acid ( 10CHO--PGA) entered the folate pool very slowly, and is thought to be relatively ineffective in nutrition. 3. 10-Formyl[2-14-C]tetrahydrofolic acid (10CHO--[2-14-C]THF) entered the folate pool very rapidly. 5-Methyl[2-14-C]tetrahydrofolate (5CH3--[2-14-C]THF) was the major urinary folate. 4. 5-Formyl[2-14-C]tetrahydrofolic acid (5CHO--[2-14-C]THF) entered the folate pool only to a small extent. 5CHO--[2-14-C]THF, given intravenously, produced no urinary 5CH3--[2-14-C]THF in the first 6 h. 5. 5,10-Methylidyne[2-14-C]tetrahydrofolic acid was metabolized to an extent which was dependant on the dose. At doses of 3 and 30 mug/kg body-weight, 5CH3--[2-14-C]THF represented 5-4 and 20% respectively of urinary folates anf for 10CHO--[2-14]PGA, the values were 16% of total urinary folates after the higher dose, and 78-5% after the lower dose. 6. Results obtained for the metabolism of 5CH3--THF varied depending on the position of the labelling: 5-14-CH3-THF gave no labelled urinary folate, the methyl group being lost rapidly. When 5CH3--[2-14-C]THF was given, it appeared as the major urinary folate. 7. Folates found in the liver after oral administration of labelled folates were identified by thin-layer chromatography; only folate monoglutamates were identified.