This model of arterial thrombosis induced by laser was used to evaluate the effect of aspirin (Aspegic®) on embolization. A partial occlusion was induced in small mesenteric arterioles (diameter 35-40 μm) with an Argon Laser. The laser induced the formation of a vessel wall lesion with damage of endothe-lial cells. Thrombus formed within seconds after the laser lesion and grew rapidly. Embolization began within the minute following the laser flash. Thrombus formation and embolization were repetitive phenomena. The duration of embolization was 6.50 ± 0.84 min in the control group. Then the thrombus became stable and partially obstructed the vessel lumen. The administration of aspirin at three doses (50, 100, 200 mg/kg) by intramuscular injection, 15 min before the laser injury, induced three different phenomena: (1) an increase of the number of laser injuries required for the thrombus formation; (2) a dose-dependent decrease in the duration of embolization, and (3) a dose-dependent decrease in the number of emboli. The highest dose injected induced the strongest reduction in the duration of embolization and the number of embo