Two experiments with sows were performed to investigate the effect of isoenergetic replacement of starch by fish oil or olive oil on concentrations of lipids in plasma and lipoproteins. The first experiment was based on a cross-over design with three periods, each lasting 16 days. Each sow was fed during one of the periods a basal ration with isoenergetic addition of (1) starch (495 g/d), (2) olive oil (221 g/d), or (3) fish oil (223 g/d) based on energetic requirement for maintainance. The second experiment was based on a cross-over design with eight periods, each lasting 16 days. In the first and in the last periods, each sow was fed the basal ration. In the other six periods, each sow was fed the basal ration with addition of two different amounts of (1) starch (284/568 g/d), (2) olive oil (140/281 g/d), or (3) fish oil (141/282 g/d). The two different amounts of addition were selected to exceed the energetic requirement for maintainance by 25% or 50%. In both experiments blood samples were taken before each change of the ration. In both experiments olive oil elevated the concentration of cholesterol in plasma in comparison with starch. This elevation was due to a large elevation in high-density lipoproteins (HDL), and a slight elevation in low-density lipoproteins (LDL) and very-low density lipoproteins (VLDL). The ratio between HDL and LDL cholesterol was increased by feeding olive oil. The effect of olive oil on concentrations of cholesterol in plasma and lipoproteins was dose-dependent. In both experiments none of the two dietary oils significantly changed concentrations of triglycerides in plasma and lipoproteins. Concentrations of phospholipids in plasma, HDL, and LDL were elevated by olive oil. In both experiments addition of fish oil elevated concentration of cholesterol in plasma due to elevated cholesterol concentration in LDL. Concentration of HDL cholesterol was not changed by fish oil. Thus, the ratio between HDL cholesterol and LDL cholesterol was lowered by fish oil. The effect of fish oil on concentration of cholesterol in plasma and lipoproteins was also dose-dependent. Fish oil had no significant effect on phospholipid concentrations in plasma and lipoproteins. In conclusion, in the present experiment olive oil caused antiatherogenic changes of the lipoprotein profile, whereas fish oil caused proatherogenic changes of the lipoprotein profile.