Abstract Choline administration increases blood choline, brain choline, and brain acetylcholine levels in rats. It also increases blood choline levels in humans and appears to be a useful treatment for some patients with tardive dyskinesia, a brain disease probably associated with deficient cholinergic tone. In order to characterize other possible metabolic and hormonal effects of choline-containing compounds, we measured changes in serum choline, glucose, insulin, cortisol, prolactin, cholesterol, and triglyceride levels resulting from ingestion of low- or high-choline meals in 16 normal human subjects. After the consumption of a single meal containing 3 g choline chloride, serum choline rose by 86% ( p < 0.01), attaining peak values after 30 min. When the same subjects ate a meal containing an equivalent amount of choline in the form of lecithin, serum choline levels rose by 33% after 30 min, and continued to rise for at least 12 hr, to 265% over control values ( p < 0.001). Serum choline concentrations were related to the amount of choline in the diet: they did not vary significantly during 24-hr periods when the subjects consumed a low-choline diet for two consecutive days, but rose substantially ( p < 0.01) after each high-choline meal. Serum glucose, insulin, cortisol, and prolactin levels were not significantly modified by choline or lecithin ingestion. Lecithin consumption increased serum triglyceride levels and lowered serum cholesterol concentration.