The mechanisms responsible for the decreased high density lipoprotein (HDL) cholesterol levels associated with obesity and insulin resistance are not well understood. Lecithin: cholesterol acyltransferase (LCAT) and cholesterol ester transfer protein (CETP) are key factors in the esterification of cholesterol in HDL and the subsequent transfer of cholesteryl ester towards apolipoprotein B-containing lipoproteins. Phospholipid transfer protein (PLTP) may be involved in the regulation of HDL particle size. We therefore measured the activities of LCAT, CETP and PLTP using exogenous substrate assays, as well as lipids, lipoproteins, insulin and C-peptide in fasting plasma from eight healthy obese men (body mass index > 27 kg m-2) and 24 non-obese subjects. The obese men had lower levels of HDL cholesterol (P < 0.05) and higher levels of plasma triglycerides (P < 0.05), insulin (P < 0.05) and C-peptide (P < 0.01), as compared to the quartile of subjects with the lowest body mass index (BMI < 22.4 kg m-2). CETP and PLTP activities were elevated in the obese men by 35% (P < 0.01) and by 15% (P < 0.05), respectively. LCAT activity was comparable among the quartiles. Linear regression analysis showed that CETP activity was positively correlated with body mass index (P < 0.02), fasting blood glucose (P < 0.05) and plasma C-peptide (P < 0.05). PLTP activity was positively related to body mass index (P < 0.01), waist to hip circumference ratio (P < 0.001), as well as to fasting blood glucose (P < 0.05) and plasma C-peptide (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)