The aim was to establish whether interesterification of oils, an alternative to the use of trans fatty acids in margarine manufacture, adversely affects plasma lipids. Twenty-seven hypercholesterolemic men participated in a double-blind, crossover trial of three margarines: 1) high-linoleic acid, moderate trans fatty acids; 2) high-palm oil blend (predominantly lauric, myristic, palmitic, oleic, and linoleic acids); and 3) an interesterified form of the high-palm oil margarine. Both high-palm oil margarines led to similar low-density-lipoprotein (LDL) cholesterol concentrations (4.43 +/- 0.94 and 4.54 +/- 0.88 mmol/L, respectively), which were significantly higher than the LDL concentrations after the high-linoleic acid margarine (4.02 +/- 0.85 mmol/L, P < 0.001). Interesterification transferred substantial proportions of palmitic acid into the sn-2 position of glycerides and unsaturated fatty acids into the sn-1,3 positions, and this was reflected in plasma chylomicrons. This study shows that interesterification of oils used to harden margarines does not raise plasma cholesterol more than does the margarine's constituent fatty acids.