Effects of electrical stimulation of the nerve bundles including sensory and parasympathetic nerves innervating cerebral arteries on cerebral blood flow (CBF) and mean arterial blood pressure (MABP) were investigated with a laser-Doppler flow meter and a blood pressure monitoring system in anesthetized rats pretreated with and without capsaicin. The electrode was hooked on the nerve bundles including distal nasociliary nerve from trigeminal nerve and parasympathetic nerve fibers from sphenopalatine ganglion. In control rats, the nerve stimulation for 30 sec increased CBF in the ipsilateral side and MABP. Hexamethonium attenuated the increase in CBF and abolished that in MABP. Under treatment with hexamethonium, N^G-nitro-L-arginine (L-NA, 1 mg/kg) significantly attenuated the stimulation-induced increase in CBF, which was restored by the addition of L-arginine. Even though the dose of L-NA was raised upto 10 mg/kg, the stimulation-induced increase in CBF was not further inhibited and was never abolished. In capsaicin-pretreated rats, magnitudes of the stimulation-induced increases in CBF and MABP were lower than those in control rats. Hexamethonium attenuated the increase in CBF and abolished that in MABP. Under treatment with hexamethonium, L-NA abolished the stimulation-induced increase in CBF in capsaicin-pretreated rats. In conclusion, nitric oxide released from parasympathetic nerves and neuropeptide(s) released antidromically from sensory nerves may be responsible for the increase in CBF in the rat. The afferent impulses by nerve stimulation may stimulate trigeminal nerve and lead to the rapid increase in MABP, which partly contributes to the increase in CBF.