Effects of tea catechins (tannins) on lipid metabolism were studied in male weanling rats fed a 25% casein diet containing 15% lard and 1% cholesterol for 28 days. Crude tea catechins prepared from green tea powder were supplemented at a 1% and 200 of the lard-cholesterol diet. The addition of 2% tea catechins slightly depressed growth but at the 1 level was without effect. Tea catechins decreased plasma total cholesterol, cholesterol ester, total cholesterol - HDL-cholesterol (VIDL-+ LDL-cholesterol) and atherogenic index (VLDL-+ LDL-cholesterol/HDL-cholesterol). Hematocrit and plasma glucose were not altered by the addition of tea catechins. The liver weight, liver total lipids and cholesterol concentrations in rats fed the lard-cholesterol diet increased more than in the control rats, but the addition of tea catechins to the lard-cholesterol diet decreased those parameters. Tea catechin supplementation increased fecal excretion of total lipids and cholesterol. The results demonstrate that tea catechins exert a hypocholesterolemic effect in cholesterol-fed rats.