Bombesin is a particularly potent inhibitor of gastric acid secretion when injected intracisternally in the rat. Because bombesin-like immunoreactivity is found in several forebrain regions implicated in gut regulation, the ability of bombesin to affect gastric secretion was tested in these areas by direct microinfusion. Bombesin significantly and dose-relatedly suppressed gastric acid secretion when it was infused into the hypothalamic paraventricular nucleus. Bombesin microinfusion into the ventromedial or lateral hypothalamic areas, or the caudate-putamen, had no significant effect. A further experiment using glass micropipets showed that back-diffusion of bombesin along the cannula track to a distant site of action was unlikely to account for the results obtained, and provided further evidence that the active site is limited to the paraventricular nucleus and possibly the ventralmost nucleus reuniens. The results suggest that the bombesin receptors and immunoreactive terminals previously identified in this region may be involved in the central regulation of gastric secretion.