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Direct gas chromatographic method for quantitative determination of plasma neutral lipids was used for the study of cholesterol esterification in vitro. Fully automated computerized method permits the determination of lipid classes (free cholesterol, cholesteryl esters, and triglycerides), as well as their fractions according to the molecular weight, without previous derivatization. All components are determined from one analysis. The method is highly precise and accurate. The coefficient of variation for free and esterified cholesterol is 1.21 and 1.11% in the concentration range 30-430 and 75-545 mg/dl, respectively. The LCAT activity was determined as a decrease in the free cholesterol concentration after one hour's incubation; from the same analysis, the recovery control as an increase in the esterified cholesterol concentration was calculated. The mean difference was 1.06%, maximum difference did not exceed 4%. The LCAT activity in the reference group was 97.2 ± 28.2 µmol/l/h and was significantly lower than that in hyperlipidemic one. Intravenous administration of heparin had an inhibition effect in subjects with hyperlipidemia of type IV, while only slight changes in the reference group and an increase in hyperlipidemia of type III were observed.