1. The lipids and lipoproteins of lymph obtained from the dorsum of the foot were examined in seven human subjects.
2. The concentration of total cholesterol in lymph was about one-tenth that in plasma and was significantly correlated with the plasma total cholesterol concentration. The ratio of esterified to total cholesterol in lymph was similar to that in plasma.
3. Triglyceride was detectable in lymph, but the concentration was less than one-tenth that in plasma and was unrelated to the plasma triglyceride concentration.
4. No lipase activity was detectable in lymph, either before or after intravenous injection of heparin.
5. Cholesterol-esterifying activity was detected in four samples of lymph.
6. The major lipoprotein antigens of human plasma (apo-A, apo-B and apo-C) were present in whole lymph, but their distribution in fractions of different density was different from that in plasma.
7. [14C]Cholesterol, injected intravenously, appeared in lymph within 30 min of the injection, indicating that some of the cholesterol in lymph is derived directly from plasma.
8. At intervals greater than 29 days after a single intravenous injection of [14C]-cholesterol, the specific radioactivity of lymph cholesterol was greater than that of plasma cholesterol, indicating that some of the cholesterol in lymph is derived from tissue pools of cholesterol with slow turnover.
