Background: A high homocysteine concentration is a potential risk factor for cardiovascular disease that can be reduced through betaine supplementation. Choline is the precursor for betaine, but the effects of choline supplementation on plasma total homocysteine (tHcy) concentrations in healthy humans are unknown. Objective: The objective was to investigate whether supplementation with phosphatidylcholine, the form in which choline occurs in foods, reduces fasting and postmethionine-loading concentrations of plasma tHcy in healthy men with mildly elevated plasma tHcy concentrations. Design: In a crossover study, 26 men ingested ≈2.6 g choline/d (as phosphatidylcholine) or a placebo oil mixture for 2 wk in random order. Fatty acid composition and fat content were similar for both treatments. A methionine-loading test was performed on the first and last days of each supplementation period. Results: Phosphatidylcholine supplementation for 2 wk decreased mean fasting plasma tHcy by 18% (-3.0 μmol/L; 95% CI: -3.9, -2.1 μmol/L). On the first day of supplementation, a single dose of phosphatidylcholine containing 1.5 g choline reduced the postmethionine-loading increase in tHcy by 15% (-4.8 μmol/L; 95% CI: -6.8, -2.8 μmol/L). Phosphatidylcholine supplementation for 2 wk reduced the postmethionine-loading increase in tHcy by 29% (-9.2 μmol/L; 95% CI: -11.3, -7.2 μmol/L). All changes were relative to placebo. Conclusions: A high daily dose of choline, supplemented as phosphatidylcholine, lowers fasting as well as postmethionine-loading plasma tHcy concentrations in healthy men with mildly elevated tHcy concentrations. If high homocysteine concentrations indeed cause cardiovascular disease, choline intake may reduce cardiovascular disease risk in humans. © 2005 American Society for Clinical Nutrition.