Background: Endothelial dysfunction caused by impaired endothelial cell regeneration is thought to be related with late stent thrombosis and chest pain in patients with drug eluting stent(DES) implantation. The aim of this study was to investigate whether intrasent neointimal growth(NG) on intravascular ultrasound(IVUS) could suggest endothelial regeneration and functional recovery or not. Methods: We analyzed 10 consecutive stented segments(Cypher: Taxus=7:3) of left anterior descending arteries in 10 patients(mean age: 60짹 9yrs, M:F=7:3) underwent routine follow-up coronary angiogram and showed no restenosis. Endothelial functions were estimated with intracoronary nitric oxide(NO) concentrations and the degrees of vasoconstriction after intracoronary injection of acetylcholine 20ugm. We graded vasoconstriction into 3 categories defined as normal response(NR)���30%, 30%< equivocal vasoconstriction(EVC)���90% and significant vasospasm(SVS)>90% of luminal vasoconstriction, respectively. The NG was estimated with IVUS under automatic pullback manner and the patients were divided into NG and no NG groups according to the presence or absence of neointimal growth. Results: 1.The mean duration from stenting to follow up angiogram was 8 months ranging from 6 to 19 month. 2. There were no differences in the degree of vasoconstriction and plasma NO concentration( Cypher : Taxus = 272짹92 : 182짹 107 umol/L, p>0.05) according to the type of stents used. 3. No NG group showed more severe vasoconstriction than NG group(table, p<0.05). 4. Intracoronary NO concentration was not different between NG and no NG group( NG : no NG = 272짹92 : 182짹 107 umol/L, p>0.05). Conclusion: Neoinitmal growth on IVUS might be a marker of endothelial cell regeneration and functional recovery in patients with DES implantation and final results having statistical power can be presented at the scientific meeting.