Objective:The purpose of this study is to determine whether the anti-atherogenic effect of L-arginine is due to an inhibition of rnacrophage infiltration and smooth muscle cell(SMC) proliferation in the pulmonary artery of hypercholesterolemic rabbits. Methods:Twenty male New Zealand white rab-bits were randomized into four treatment groups:Group AC with 1%cholesterol diet supplemented with 2.25% L-arginine HCl in the drinking water(AC,n=5),Group MC with 1%cholesterol diet supplemented with 0.9%methionine in the drinbing water(MC,n=5),Group C with 1%cholesterol dietonly(c,n=5),and Group NC with normal diet(NC,n=5).After 10 weeks the blood samples were collected for biochemical studies,and the main pulmonary arteries were harvested for histomor-phometry and immunohistochemical studies. Comparison between two means are analyzed using the Student’s test.Comparison of more than two means is performed using analysis of variance. Results:The results showed that dietary L-arginine supplernentation reduced the intimal thickness(from 1. 94 to 0.67mm2)and accumulation of macrophages(75%～13%, P <0. 01),and inhibited the SMC prolif-eration(68%～21.3%,P <0.01)significantly in association with anti-atherogenesis without affecting plasma cholesterol level; Supplementation of methionine did not produce such effects(75%vs 73.3%and 68 vs 70.8%).Conclusion : Dietary supplementation of L-arginine can inhibit atherogenesis in hy-percholesterolemic rabbits,The anti-atherogenic effect of L-arginine is largely due to the inhibition ofmacrophage infiltration and SMC proliferation.