Effects of microiontophoretically applied transmitter receptor antagonists on the evoked response of “pain” units of PVN in rats by sciatic stimulation were observed. The results showed: (l)The evoked response of 7 out of 38 PVN “pain” units could be blocked by atropine (7/38); 5 out of 27 by hexamethonium; 6 out of 31 by phentolamine (6/31); and 4 out of 25 by propranolol (4/25). Seventeen out of 52 were blocked by cyproheptadine (17/52), but 3 out of 52 were augmented by cyproheptadine (3/52). (2) The evoked response of the same “pain” unit could be blocked by two antagonists: the evoked response of 2 out of 27 PVN “pain” units could be blocked by atropine and cyprohepadine; 3 out of 20 by hexamethonium and cyproheptadine; 2 out of 25 by prepamolol and cyproheptadine. These results suggest that the noxious somatic input to PVN involves 5-HT, cholinergic and adrenergic transmitter receptor mechanisms and that the convergence of various transmitter systems on PVN “pain” unit is indicated.