The role of endogenous nitric oxide (NO) in the gastric microcirculation of the anaesthetised rat was investigated using the selective inhibitor of NO synthesis, N^G-monomethyl-L-arginine (L-NMMA). L-NMMA (12.5–50 mg kg⁻¹ i.v.) induced a dose-dependent increase in systematic arterial blood pressure (BP) and fall in resting gastric mucosal blood flow (MBF), as estimated by hydrogen-gas clearance. The effects of L-NMMA on BP and MBF were abolished by concurrent administration of L-arginine. The enantiomer D-NMMA had no effect on resting BP or MBF. These findings indicate that endogenous NO, derived from L-arginine, plays a local vasodilator role in the gastric mucosal microvasculature.