The composition of serum high-density lipoproteins (HDL) was studied in 64 patients with polypous cholesterosis (PC). The spectrum of serum lipids in patients with PC was characterized by the lower concentrations of HDL cholesterol (42.0 +/- 2.5 mg/dl; p < 0.05) and higher concentrations of low-density lipoproteins (LDL) cholesterol (169.9 +/- 6.9 mg/dl; p < 0.01) than those in the controls. The decreased HDL cholesterol, or hypoalphacholesterolemia was associated with quantitative changes in HDL phospholipids (PL) (66.48 +/- 3.4; p < 0.01) and with changes in the composition of individual PL by lowering the proportion of lecithin (47.13 +/- 2.19 mg/dl; p < 0.01). It may be suggested that the lower amount of HDL cholesterol is caused by the decreased HDL acception of free cholesterol from the peripheral cell membranes due to the impaired complexation of PL with free cholesterol and associated the altered PL composition of the superficial monolayer of a lipoprotein particle. At the same time the physicochemical changes in Hdl superficial layer are a cause of abnormal free cholesterol esterification and the impaired plunge of esterified cholesterol into the nucleus of a HDL particle, which facilitates the conversion of HDL to LDL and may explain elevated LDL levels in cholesterosis. The findings suggest that serum lipids are involved in the development of cholesterosis.