Background: Web-like (W) and membrane-like (M) structures have been observed on coronary stent edges on angioscopy but their incidence and mechanisms remain obscure. Methods and Results: First, 26 patients [acute coronary syndromes (ACS) in 10 and stable angina (SA) in 16] underwent angioscopy of the stented coronary artery immediately after, and 32 patients (ACS in 18 and SA in 14) 6 months after insertion of bare-metal stents. Second, angioscopy of the stented coronary artery was performed in 4 beagles 5 h after, and in 9 beagles 1 month after stenting. W and M were observed in patients with ACS and those with SA (80.0% vs 18.7%; P<0.05) immediately after and 6 months after stenting (55.5% vs 28.5%; NS). They were stained with Evans blue that selectively stains fibrin immediately after stent insertion, but not 6 months later. In beagles, W and M were observed in 75.0% at 5 h and in 66.6% 1 month later. Histologically, W and M were composed of fibrin at 5 h, whereas they were composed of collagen fibers at 1 month. Conclusions: W and M were frequently formed on the edges of coronary stents. They were formed with fibrin in the acute phase, whereas this fibrin was replaced by collagen fibers in the chronic phase.  (Circ J 2010; 74: 1830 - 1836)