The absorption and oxidation of carboxyl-labeled octanoic acid as determined by monitoring of expired C14O2 was studied in 27 subjects. In 12 normal volunteers there was no significant difference in the recovery of C14O2after oral and intravenous administration of the isotopically labeled octanoic acid. Administration of 100 g glucose by mouth did not seem to inhibit octanoic acid oxidation in ten subjects. Infusion of 1 g unlabeled octanoate also did not significantly affect the oxidation of radioactive octanoate in five subjects. These observations in humans tend to confirm animal studies which have shown that octanoic acid is well absorbed from the gastrointestinal tract and rapidly oxidized. The oxidation of small amounts of this fatty acid appears to proceed at the same rate despite moderate blood levels of glucose or octanoic acid. These characteristics of short chain fatty acid absorption and oxidation can be exploited in the study of fat absorption in human subjects. intestinal absorption; fatty acid metabolism Submitted on August 14, 1963