Objective Histamine is one of the most important neurotransmitters in the brain and cell bodies of the histaminergic neurons are located exclusively in the tuberomammillary nuclei of the hypothalamus.Their efferent varicose fibers project predominantly ipsilateraly to the whole central nervous system,including most subcortical nuclei and the cerebral cortex.Our previous studies,together with other data,have showed that the H1,H2 receptors have expressed in the intracortical blood vessels of rat brain,suggesting that histamine could regulate the activity of intracortical microvessels in brain.We also found that histamine could make the intracortical microvessels contract via the H1 receptor on the rat brain slice.In this paper,the effect of histamine on regional cerebral blood flow (rCBF) in the rat parietal lobe was detected by the laser-Doppler flowmetry (LDF).