The effects of intracerebroventricular and intravenous injection of neurotensin on gastrointestinal and colonic motility were examined in fasted and fed conscious, intact, and vagotomized dogs. When administered intracerebroventricularly at 20 ng X kg-1 or higher doses in the fasted state, neurotensin reduced the duration of the periods of gastric motility for 3-4 h. During this time the jejunal migrating motor complex was replaced by isolated phases of regular activity occurring at a rhythm of 2-3/h, while colonic motility was unaffected. These effects were abolished after vagotomy and were not observed for 25 times higher doses when administered intravenously. Injected intracerebroventricularly at a dose of 100 ng X kg-1 30 min after a meal, neurotensin significantly reduced (P less than 0.01) the duration of the fed pattern (2.7 +/- 0.7 vs. 8.7 +/- 1.2 h for control); this effect was not observed when neurotensin was administered intracerebroventricularly 20 min before or 120 min after a meal or when injected intravenously. Systemic administration of neurotensin at a dose of 500 ng X kg-1 significantly increased (P less than 0.05) during 2 h the colonic motility indexes in both fasted and fed dogs before and after vagotomy. It is concluded that neurotensin can act i) centrally to control the pattern of antral and jejunal motility in the fasted and fed dogs, these effects being mediated by the vagus; and ii) peripherally to control the pattern of colonic motility, this response being unaffected by vagotomy.