Local excitation of neurons at the site of termination of gastric vagal afferents in the nucleus tractus solitarii (NTS) alters gastric pressure. Microinjection of one putative satiety peptide bombesin into NTS increases pressure while substance P lowers it. Therefore, we sought to determine the effects of the microinjection of cholecystokinin octapeptide (CCK-8) from micropipettes placed stereotactically into the NTS of anesthetized rats with balloons placed in the gastric antrum to sense gastric pressure waves. Sulfated CCK-8, but not nonsulfated CCK-8, produced dose-dependent decreases of gastric pressure, transient blockade of phasic waves, and subsequent dysrhythmic phasic activity. The effects were specifically related to injections into NTS and did not occur with injections given intravenously, intracisternally, or into tissue adjacent to NTS. These results support a role for CCK-8 in central regulation of not only tonic gastric pressure but also phasic activity and gastric motility.