We demonstrated earlier that in a photochemically induced thrombotic occlusion model, a reperfusion-like phenomenon may be involved in the progress of brain damage. Therefore, we now investigated changes in local cerebral blood flow in a photochemical model compared with changes in a thermocoagulated occlusion model, using autoradiography. At 5 min, and 3, 6 and 24 h after middle cerebral artery occlusion, local cerebral blood flow was measured by intravenous injection of 4-iodo[N-methyl-14C]antipyrine (20 mu Ci). In the ischemic core zone, the reduction in blood flow was similar in the two models. However, blood flow in the ischemic border zone in the photochemical model decreased transiently in the third hour after ischemia and then increased again, while the blood flow in a thermocoagulated model continued to decrease. Time courses of brain damage formation in both models were no different up to 24 h. These findings suggest that the transient reduction in cerebral blood flow in the third hour following ischemia may contribute to a reperfusion-like phenomenon in a photochemical model.