Aim To well understand the molecular events governing smooth muscle cell (SMC) prolileratlon In develt,pment of atherosclerosis (As), We investigated SMC ultrastructure and levels of c-ny proto-oncogene transcription in plaque.Matt.for 25 bealthy male Japan bigrear white rab bits were divthed control group (n = b, normal diet ) and experimental group (n = 2O, high cholesterol diet plus belloon deendothelialication) at random. The experimental group animals were carried balloon-in-jUry to aorta with 3F Fogarty catllt.r after being fed atherogenic diet for one week- We observed morpl:o-logical changes of rabbit dorta through microscoPe and ultrostructure of SMC with transmissive electrcn-mi-mpe and asse8sed the levels of c-op mRNA witb Northern blot at 1' 2. 4 and 6 weeks Postangloplasty.ReSultS bondothelialization of rabbit aorta in-dutal a large of SMC to migrate from medium to reointimal and proliferate. The changes of SMC pheotyPe were observed one week after injury. Dering 2~4 weeks, there were a nulllber of prolifcrative SMC in thickening neointima. These SMC displayed 'syn- tkftic' pheotype which cotained large amtlllnts of roue,doplasndc reticulum, free rlbosonlts, mito-ckondrla and littie contractile appartus. Some lipid-droplet in some synthetic SMC were observed. Then the typic atheroma plaque in rabbit aorta formed at 6 weeks. The predominant cell typpe in these plaqes were the SMCderived fem cell which filled witb lipiddroplet and contained a few cellular organel-lae. The levels of c-mM mRNA increased signifi-cantly at one weeks after injury Prior to SMC prolifer-ation. Then c-myc expression gradually decreased at 2,4 and 6 weeks, but the levels of c-mp mRNA at 6 weeks was still higher than that of control group.CoecIasloas Deendothelialization promotfd forma-tion of As, c-myc gene expression were closely related to SMC proliferation in development of As.