The effects of 12 weeks eicosapentaenoic acid (EPA) administration (2.7 g/day) on plasma lipoprotein subfraction levels and on activities of lecithin: cholesterol acyltransferase (LCAT) and lipid transfer protein (LTP) were investigated. Plasma VLDL-C, VLDL-TG, VLDL-PL, VLDL-apo B, VLDL-apo C-II and VLDL-apo C-III levels were decreased by 32.8% (P less than 0.05), 31.2% (P less than 0.01), 31.5% (P less than 0.05), 32.5% (P less than 0.05), 34.7% (P less than 0.05) and 34.1% (P less than 0.05), respectively. EPA did not change plasma IDL-TC, IDL-TG, IDL-PL and IDL-apo B levels. Plasma large, light LDL (LDL1)-TC, LDL1-PL and LDL1-apo B levels were decreased by EPA by 18.7% (P less than 0.02), 19.1% (P less than 0.01) and 23.3% (P less than 0.01) while LDL1-TG level was not changed. Plasma small, heavy LDL (LDL2)-TC level was increased by 25.7% (P less than 0.02) while LDL2-TG, LDL2-PL and LDL2-apo B levels were not altered. Plasma HDL2-TC, HDL2-TG, HDL2-PL and HDL2-apo A-I levels stayed unchanged by EPA treatment. EPA did not affect plasma HDL3-TC, HDL3-PL and HDL3-apo A-I levels but decreased HDL3-TG level significantly (P less than 0.02). LCAT activity was not altered by EPA. LTP activity was increased by 24.8% at 4 weeks (P less than 0.02) and by 32.1% (P less than 0.001) at 12 weeks EPA treatment. We conclude that EPA reduces plasma large, light LDL levels as well as plasma VLDL amounts and stimulates LTP activities.