Single fiber rcording technique and tail flick test of rat were used in thepresent study. The unit discharges evoked by mechanical stimuli and tail flicklatency responsed to noxious heat stimuli as indices of the activity of polymodalnociceptor were examined during and after sympathetic stimulation. Stimula-tion of the peripheral end of the lumbosaeral sympathetic trunk increased thedischarges of polymodal nociceptors at first and then inhibited markedly. Thedepression of the unit discharges lasted for more than ten min. Injection of