Phytosterols (plant sterols), abundant in fat-soluble fractions of plants, are consumed at levels of 200-400 mg/day in Western diets. Chemically resembling cholesterol, phytosterols inhibit the absorption of cholesterol. Phytosterol consumption in human subjects under a wide range of study conditions has been shown to reduce plasma total and low density lipoprotein (LDL) cholesterol levels; however, the response varies widely. Greater cholesterol-lowering efficacy occurs with consumption of the saturated phytosterol sitostanol versus sitosterol or campesterol. Most studies report no effect of phytosterol administration in high density lipoprotein (HDL) cholesterol or triglyceride levels, although certain evidence exists for an HDL cholesterol raising effect of sitostanol. Phytosterol absorption is limited, although serum phytosterol levels have proven to be important indicators of both cholesterol absorption and synthesis. Serum phytosterols correlate with HDL cholesterol level. In addition, higher phytosterol/cholesterol ratios appear in HDL versus LDL particles, suggesting the existence of an intrinsic phytosterol action, in addition to the extrinsic effect on cholesterol absorption. In conclusion, addition to diet of the phytosterol sitostanol represents an effective means of improving circulating lipid profiles to reduce risk of coronary heart disease.