Retrograde infusion of hyperthermic saline solution at 43 degrees C into the left external carotid artery increases cerebrovascular permeability to Evans-blue albumin in the left cerebral hemisphere in normothermic Wistar rats. Isotonic saline solutions at 37 degrees C for Group I and at 43 degrees C for Group II were infused for 30-s at a constant rate of 0.12 ml/s into the left external carotid artery. All animals receiving hyperthermic saline perfusion, had disturbed blood-brain barrier permeability. Based on visual inspection, disruption grade in the left hemispheres of 6 out of 10 animals were 3+. Mean values for Evans-blue dye were found to be 0.28+/-0.06 mg% in left hemisphere after normothermic saline infusion (Group I), and 2.4+/-0.5 mg% in the same hemisphere after hyperthermic saline infusion (Group II). The difference was found to be significant between Group I and Group II (P<0.01).