Cholesterol removal from tissues into HDL depends on the activity of lecithin-cholesterol acyltransferase (LCAT; E.C. 2.3.1.43) that is associated with lower cardiovascular diseases risk. HDL cholesterol concentration and LCAT activity can be modulated by dietary fatty acids. Original data with substrate models have shown a positive effect of myristic acid (MA) on the esterification rate of cholesterol. The purpose of this study was to examine the effect of moderate intakes of MA associated with recommended intake of alpha-linolenic acid (ALA) on LCAT activity in humans. Two experimental diets were tested for 3 months each. Diet 1-MA 1.2% of total energy (TE) and ALA 0.9% TE, diet 2-MA 1.8% and ALA 0.9% TE; a control diet (MA 1.2% and ALA 0.4% TE) was given 3 months before diet 1 and diet 2. The endogenous activity of LCAT was determined at completion of each diet. Compared with the control diet (13.2 +/- 3.1 micromol CE/(L x h)), LCAT activity increased significantly (P < 0.001) with diet 1 (24.2 +/- 3.6 micromol CE/(L x h)) and diet 2 (33.3 +/- 7.4 micromol CE/(L x h)); the increase observed with diet 2 was significantly (P < 0.001) greater than that due to diet 1. These results suggest that ALA (from rapeseed oil, mainly in sn-2 position) and MA (from dairy fat, mainly in sn-2 position) favor LCAT activity, by respective increases of 83 and 38%. When they are supplied together, a complementary effect was observed (average increase of 152%). Moreover, these observations were associated with a decrease of the ratio of total to HDL-cholesterol. In conclusion, our results suggest that moderate supply of MA (1.8% TE) associated with the recommended intake of ALA (0.9% TE) contributes to improve LCAT activity.