Serum levels of high-density lipoprotein cholesterol are often increased in patients with primary biliary cirrhosis. To elucidate the mechanism of the elevation of high-density lipoprotein cholesterol levels in this disease, lipoprotein abnormalities were analyzed in 10 patients subdivided into two groups according to concentration of high-density lipoprotein cholesterol. Activities and protein masses of lipoprotein lipase, hepatic triglyceride lipase and cholesteryl ester transfer protein were also determined. Serum highdensity lipoprotein cholesterol concentration exceeded 90 mg/dl in 5 of 10 patients. Lipoprotein particles in the high-density lipoprotein, fraction (with density between 1.063 and 1.125 gm/ml) were enriched with apolipoprotein E and larger in size than those of normal controls. In patients with and without hyperalphalipoproteinemia, hepatic triglyceride lipase activity was significantly decreased (p < 0.05); this was due to the reduction of its protein mass. Lipoprotein lipase activity and protein mass were normal. It is noteworthy that increases in cholesteryl ester transfer protein activity andmass were observed. The enhancement of cholesteryl ester transfer protein activity was more remarkable in the patients with hyperalphalipoproteinemia than in those without hyperalphalipoproteinemia. Because a significant positive correlation was demonstrated between activity and protein mass (r = 0.90, p < 0.001), the increase of cholesteryl ester transfer protein activity may be attributed to the increase of its protein mass. These data suggest that the decrease of hepatic triglyceride lipase levels at least partly explains the appearance of apolipoprotein E-rich large high-density lipoprotein particles in patients with primary biliary cirrhosis.