The effect of sex hormones on serum lipoproteins is best illustrated by the pronounced differences in lipid and lipoprotein profiles between adult men and pre-menopausal women. Men present with higher total serum and LDL cholesterol, higher serum TAG, and lower HDL cholesterol concentrations than premeno-pausal women. This difference in lipid profiles confers protection against CHD on premenopausal women so that their CHD risk lags some 10 years behind that of men of the same age. This applies until estrogen failure at the menopause, when CHD risk in women overtakes that of men. Estrogen was the first com-pound shown to stimulate LDL receptor activity in cell culture, an effect that not only accounts for lower LDL levels in women but also the sharp increase in LDL cholesterol after the menopause, to levels above those of men. Estrogens also stimulate the pro-duction of TAG and VLDL, but any adverse effects must be outweighed by the efficiency of TAG removal mechanisms that maintain lower serum TAG levels in women than in men until the menopause. In addition to these effects, estrogen selectively inhibits the activ-ity of HL, which contributes to the HDLs in women. In direct contrast, the androgenic male hormone tes-tosterone suppresses LDL receptor activity, raising LDL cholesterol. It is also a powerful stimulant of HL activity, and is responsible for lowering HDL choles-terol in men, most notably in male body builders on anabolic steroids, in whom serum HDL can be almost absent.