Aim To identify possible mechanisms of the sug-gested high atherogenicity of lipoprotein (a) [LP(a)],the susceptibility of LP (a) to Cu2+-induced oxidation and its effects on proliferation of rabbit aortic smooth muscle cells (SMC) were studied and compared with those of low density lipoprotein (LDL).Methods Human Lp(a) and LDL were isolated and purified from normal blood plasma by ultracen-trifugation, sephacryl S-400 gelpermeation chromatog-raphy. The oxidative modification of Lp(a) and LDLwas identified by agarose gel electrophoresis and thio-barbituric acid reacitive substance(TBARS) method.Cell counting and 3H-TdR incorporation were used to observe the mitogenic effect of lipoproteins and oxi-dized lipoproteins on SMC.Results The susceptibility of LP (a) to oxidation was lower than that of LDL. Native Lp(a) and LDL induced slight increase in number of SMC and 3H-TdR incorporation respectively, which was statistically in-significant (P>0. 05); ox-Lp(a) and ox-LDL promot-ed the increase of cell number and DNA synthesis significantly (P<0. 01), and the promoting effects were greater than those of the corresponding native lipoproteins (P<0. 05, P<0. 01).Conclusion Oxidized LP (a) might play a role in atherogenesis through stimulating the proliferaion of SMC.