OBJECTIVE To study the effect of microinjection L-arginine, a precursor for the synthesis of nitric oxide into the functionally identified caudal pressor area (CPA) in ventral surface of medulla oblongata. METHODS Artery pressure (AP), renal perfusion pressure (RPP) and heart rate were recorded to study the effects of microinjection of NO related drugs into CPA. RESULTS (1) Unilateral microinjection of L-arginine (60 - 100 nmol) into CPA produced prominent dose-related depressor and bradycardic effects and reduced renal perfusion pressure. (2) Unilateral microinjection of L-arginine (100 nmol) 3 min after microinjection of methylene blue (10 nmol) into CPA did not significantly change AP and RPP. (3) Unilateral microinjection of L-glutamate (350 nmol) into CPA elicited pressor effect which was significantly dose-related attenuated by prior microinjection of L-arginine (60-100 nmol) into the same area. CONCLUSIONS Theses results suggest that L-arginine-NO pathway in the CPA participates in the central regulation of arterial pressure and may have a key role in the inhibiting of glutamatergic neurotransmission in the anesthetized rats.