To study the influence of induced hypertension in acute phase on the infarct volume and regional cerebral blood flow (rCBF) during focal cerebral ischemia in rats. The adult rat's models of permanent focal cerebral ischemia were established by permanent middle artery occlusion. Thirty-six rats were divided six groups. The rCBF of cortical penumbra during focal cerebral ischemia was determined by Laser-Doppler Flowmetry. After experiment was over, the brain was TTC stained and the infarct volume was calculated by computer image analytic system. The rCBF was resumed by (81.8 +/- 3.1)%, (56.0 +/- 2.1) and (38.8 +/- 2.0)% in induced hypertension groups compared with the basic rCBF. The volume of infarction was (14 +/- 7) mm(3), (90 +/- 24) mm(3) separately in group induced hypertension after 2 and 3 hour ischemia. Induced hypertension during 3 hours could reduce infarct volume significantly. To improve rCBF in penumbra may be one of protective mechanism of induced hypertension on brain ischemia.