Neuropeptide Y (NPY) was injected into the paraventricular nucleus (PVN) of the hypothalamus of anesthetized rats in order to assess its effect on gastric acid secretion. NPY evoked a dose-dependent decrease of interdigestive gastric acid output when injected directly into the PVN or immediately ventral to it. Intracerebroventricular NPY and saline injections did not alter acid output. Injection of NPY into adjacent non-PVN hypothalamic areas resulted in either an elevated acid output or had no effect depending on the site of injection. Mean arterial blood pressure and heart rate were not consistently affected by NPY. These results show that injection of NPY into the PVN of anesthetized rats inhibits interdigestive gastric acid output in a dose-dependent manner.