The effect of LPSw (a lipopolysaccharide from wheat flour) on cholesterol catabolism was examined using WHHL (Watanabe heritable hyperlipidemic) rabbit, which is an experimental model of familial hyperlipidemia. The serum cholesterol level of the animal decreased by the addition of LPSw to drinking water. Following cessation of the addition of LPSw to the drinking water, the cholesterol level was decreased for 30 to 40d and then gradually elevated. The serum level of apolipoprotein B, which is a constituent of apolipoprotein of low density lipoprotein (LDL), also decreased in accord with serum cholesterol at a nearly coincident rate. Conversely, the level of apolipoprotein A-I, which is a constituent of apolipoprotein of high density lipoprotein (HDL), did not change, nor did HDL-cholesterol. Furthermore, the atherosclerosis risk factor, expressed as the ratio of apolipoprotein B to apolipoprotein A-I, was decreased by LPSw administration.