In lymph from the dorsum of the foot of 8 patients with primary hyperlipoproteinaemia, who ate diets low in animal fat supplemented with maize oil, and from 3 normal subjects, the total cholesterol concentration was about a tenth of that in plasma and showed a significant correlation with plasma total cholesterol; the ratio of esterified to total cholesterol was similar in lymph and plasma. Triglyceride was detectable in lymph but was less than one-tenth that in plasma and was unrelated to plasma triglyceride concentration. No lipase activity was detectable in lymph either before or after intravenous injection of heparin. Radioactivity was detected in lymph cholesterol-14C indicating that some of the cholesterol in lymph was derived from plasma. At long intervals, greater than 29 days, after intravenous injection of cholesterol-14C, the specific radioactivity of lymph cholesterol was greater than that of plasma cholesterol, indicating that some of the cholesterol in lymph was derived from tissue pools of cholesterol with slow turnover.