The effects of treadmill exercise on hepatic cholesterogenesis and fecal steroid excretion were studied using male Wistar rats fed a commercial pellet ration. Exercise, in comparison with ad libitum or pair-feeding sedentary groups, caused the following significant changes: (i) a reduction in the concentration of plasma triglyceride, phospholipid and cholesterol; (ii) a reduction in liver weight; (iii) increases in hepatic 3-hydroxy-3-methylglutaryl-CoA reductase activity and incorporation of mevalonate into digitonin precipitable sterol; (iv) increases in excretion of neutral and acidic steroids into the feces; (v) the increase in lipoprotein lipase activity in the cardiac muscle, and (vi) the decrease in the concentration of carcass triglyceride but not of cholesterol. These data suggest that the mechanism responsible for the plasma cholesterol-lowering effect of exercise is attributable to an increase in excretion of fecal neutral and acidic steroids accompanied by an acceleration of cholesterol turnover in the body.