Relationships between plasma levels of lipoproteins and sex hormones were studied in 24 healthy premenopausal women with no risk factors for coronary heart disease. The women were carefully selected to remove the effects of other environmental factors, such as smoking, drugs, alcohol, and exercise, which are known to influence lipid metabolism. They all ate precisely the same Western-style diet for 1 to 2 weeks before blood samples were obtained in the follicular phase of their menstrual cycle. After adjusting for other hormones by multiple regression, significant positive partial correlations were seen between high density lipoprotein cholesterol (HDL-C) and protein bound estradiol (r = .57, P = .02), as well as between very low density lipoprotein cholesterol (VLDL-C) and protein bound estradiol (r = .63, p = .01). A significant negative partial correlation was seen between VLDL-C and free estradiol (r = -.65 P = .01). Conversely, low density lipoprotein cholesterol (LDL-C) levels were negatively correlated with protein bound estradiol (r = -.77, P less than .001) and positively correlated with free estradiol (r = .71, P less than .001). No associations between plasma lipoproteins and testosterone were seen; however, androstenedione was positively correlated with VLDL-C (r = .59, P = .01). These findings show a close link between plasma lipoproteins and sex hormones, and may help to explain the lower risk of coronary heart disease in women.