Besides causing functional and clinical damage, hypercholesterolaemia also causes morphological alterations of vascular endothelium. Rabbits fed a diet with 1% cholesterol for 4, 6, or 8 weeks are experimental models for hypercholesterolaemia, with pathological structural changes in vascular luminal surface. Morphological investigation by scanning electron microscopy was performed to reveal the tridimensional growth of these lesions and the differences in this growth induced by concomitant dietary assimilation of fish-oil (2 g/day). Macroscopic reduction in fatty-streak production was clearly seen in rabbits fed fish-oil. Scanning electron microscopy confirmed that the area of intimal lesions was only 21 +/- 6% in this group, while in the group fed cholesterol without fish oil, the lesioned area attained 76 +/- 5%. Endothelial swelling was less marked, probably due to reduced intracellular lipid accumulation into the foam cells. Adherent macrophages were also fewer. The differences might be correlated with protection against the lipoproteins' atherogenic effects and to hemorheological benefits produced by the Omega-3 fatty acid (85%) present in fish-oil.