Medium-chain triglycerides (MCTs) have been introduced as lipid substrates in parenteral nutrition because of their rapid and complete oxidation. Although there are many clinical studies on the use of MCTs in parenteral nutrition there are only a few studies on their kinetics; most of these studies used indirect methods (such as light scattering) to determine MCT concentrations in plasma. We determined the hydrolysis rate of MCTs to medium-chain fatty acids (MCFAs) and the disposition rate of MCFAs in nine healthy volunteers who received an intravenous bolus of MCTs as 10% MCT + 10% long-chain triglyceride solution. MCTs and MCFAs were analyzed by gas-liquid chromatography. One linear compartment model was used and its parameters were numerically estimated. The first-order transformation constant of the hydrolysis step from MCT to MCFA was 0.0964 +/- 0.0152 min-1(for 8- and 10-carbon pooled together); the rate constant for tissue MCFA uptake from plasma was 0.0725 +/- 0.0230 min-1. The apparent volumes of distribution were about 4.5 L for MCT and 19 L for MCFA in a typical 70-kg subject. The plasma half-life of MCT was 11 min and that of MCFA was 17 min. The limiting step in the clinical use of MCTs seems to be tissue uptake of MCFAs.