OBJECTIVE The effects of thrombotic occlusion of the middle cerebral artery on compromised ischemic tissue may be different from and more severe than those of cerebral ischemia induced by mechanical occlusion of the artery. Photothrombosis, which is based on photochemical damage to the endothelium and subsequent platelet aggregation, is an efficient method to induce thrombosis in vivo. This study aimed to improve and simplify this unique method for an ischemia model of middle cerebral artery occlusion in rats. METHODS Male spontaneously hypertensive rats (5 to 6 months old, 300 to 450 g) were anesthetized with halothane, endotracheally intubated, and mechanically ventilated. A krypton laser operating at 568 nm was used to irradiate the exposed distal middle cerebral artery with an intact dura above the rhinal fissure. The photosensitizing dye rose bengal (20 mg/kg body wt) was administered intravenously over 90 seconds starting simultaneously with 4 minutes of laser irradiation at a power of 20 mW to cause thrombotic occlusion of this artery. RESULTS The irradiated middle cerebral artery was completely occluded by intraluminal thrombi within 3 minutes after simultaneous laser irradiation and rose bengal infusion. Thrombosed materials were not stained by phosphotungstic acid-hematoxylin stain (ie, aggregated platelets lacked apparent fibrin). The mean volume of 3-day-old infarction, indicated by the lack of staining with 2,3,5-triphenyltetrazolium chloride, was 84.8 +/- 17.4 mm3 (mean +/- SD, n = 6). CONCLUSIONS We demonstrated a reproducible and minimally traumatic model of brain infarction induced by the thrombotic distal middle cerebral artery occlusion in rats.