We investigated the adipogenic effects of high-fat diets with different fat sources, as well as their influence on hypothalamus NPY content (NPY) and plasma corticosterone (Cs) and leptin (Lep) concentrations. In a 6-wk experiment performed in 28 male Wistar rats, high-fat diets (approx 60% of energy as fat) containing sun-flower oil (S), rapeseed oil (R), palm oil (P), or lard (L) as the fat source were applied. Carcass composition was analyzed by standard methods; NPY, Cs, and Lep were determined by RIA method. Gas chromatography was applied to measure fatty acid composition of dietary fats. S group had the highest body fat content and Lep and the lowest Cs and NPY, while L rats had high Lep and the highest Cs and NPY. W e conclude that the fatty acid composition of dietary fat is of high importance where effects of high fat diets on adiposity, as well as on plasma levels of both hormones and hypothalamus NPY content are concerned.