ABSTRACTSince platelet accumulation may be an important determinant of restenosis after angioplasty, the time course of 11Cr-labeled platelet accumulation after experimental angioplasty was evaluated in a deendothelialized, hypercholesterolemic rabbit preparation of atherosclerosis. Marked platelet accumulation (39.5 ± 8.7 × 106 platelets/1 cm vessel length) was observed at 30 min and remained active until 4 hr after angioplasty. Total accumulation over 24 hr was 56.4 ± 4.7 × 106 platelets/1 cm length. Histologic dissection was directly related to the degree of platelet accumulation, with 64 ± 15 x 106 platelets/1 cm in the group with marked dissection and 8.7 3.7 × 106 platelets/1 cm in the group with minimal dissection (p > .05). Increasing angiographic dissection also resulted in a trend toward increased platelet accumulation, and angiographic change in luminal diameter showed a significant correlation with platelet accumulation. It is concluded that marked platelet accumulation occurs early after transluminal angioplasty and is related to the extent of dissection. Restenosis may result from a complex interaction of platelet accumulation, vascular damage, and blood flow.