1. The mass of the extravascular pool of low-density lipoprotein (LDL) in liver was measured in rats injected intravenously with radioiodinated LDL by determining the radioactive iodine remaining in the extravascular tissues of liver and in plasma when the hepatic intravascular and extravascular radioactive iodine had equilibrated (equilibrium-time method). 2. The mass of the extravascular pool of LDL in the liver was about 6% of the total intravascular pool. Total extravascular pool of LDL in eight rats, obtained by multicompartmental analysis of the time-curve of disappearance of radioiodinated LDL from blood plasma, was 43 +/- 15% (mean +/- SD) of the intravascular pool. 3. Hence the hepatic extravascular pool comprises only about 14% of the total extravascular pool of LDL in the rat.