Six lactating Holstein cows were used in a replicated 3 x 3 Latin square design to determine the effects of medium-chain triglyceride supplementation on milk fatty acid composition and plasma energy metabolites. Treatments were no supplemental triglyceride, 500 ml of odd-carbon, medium-chain triglyceride (fatty acid composition: 100% pelargonic acid), or 500 ml of even-carbon, medium-chain triglyceride (fatty acid composition: 65% caproic acid, 35% capric acid) added daily to a total mixed ration. Medium-chain triglyceride supplementation did not affect ruminal molar proportions of acetate or propionate but slightly increased the molar proportion of butyrate. Even-carbon and odd-carbon, medium-chain triglycerides reduced DM intake by 1.7 and 1.3 kg/d, respectively, but did not affect milk yield or milk protein percentage. Cows that did not receive supplemental triglyceride produced milk with 3.29% fat. Milk fat concentration was increased by even-carbon, medium-chain triglyceride supplementation relative to odd-carbon, medium-chain triglyceride supplementation (3.44 vs. 2.99%). Although changes in milk fatty acid composition were observed, they were minor and mostly unexplained. Feeding even-carbon, medium-chain triglycerides caused slight increases in plasma glucose and nonesterified fatty acid concentrations, but plasma beta-hydroxybutyrate concentration was not affected by treatments. Odd-carbon, medium-chain triglyceride supplementation (500 ml/d) does not appear to be antiketogenic.