In New Zealand rabbits subjected for a 2 month period to a 1% or 2% hypercholesterolic diet, larger intimal involvement and histologically heavier lesions were observed in the animals on a hypercholesterolic diet. The intimal involvement was larger in the aortic arch. In groups of rabbits simultaneously subjected to similar diets and to i.v. CDP-choline injections, the intimal involvement appeared reduced (p less than 0.01) both in the arch and in the descending tract of the thoracic aorta.