There is considerable epidemiological evidence that tea drinking lowers the risk of heart disease. However, the mechanism by which tea can be protective is unknown. Hamsters were fed a normal or high cholesterol diet for 2 weeks and drank green or black tea ad libitum. The plasma lipid profile was significantly improved by both teas compared to controls. Also in vivo lipid oxidation as measured by plasma lipid peroxides and LDL+VLDL oxidizability were significantly decreased by the teas. In the normal fed tea groups fibrinogen was decreased but not in the high cholesterol groups. Green tea was significantly more effective than the black tea. These results show in the hamster model that black and green tea improve the risk factors for heart disease by both hypolipemic and antioxidant mechanisms and possibly a fibrinolytic effect.