In order to observe the plasma gastrin, secretin and pancreatic polypeptide (PP) levels in an acid hypersecretion state, the pyloric antrum was transposed onto the transverse colon in 4 mongrel dogs with a Heidenhain pouch. The effects of meal and cimetidine on these gut hormones and acid secretion levels were observed for 6 hr after meals. After antrocolic transposition (ACT), hypersecretion of acid and high plasma gastrin levels were observed both in the fasting and stimulated states. Plasma secretin levels were elevated for 6 postprandial hr, but were reduced by cimetidine as a result of marked suppression of acid secretion. Plasma PP levels also increased for 6 postprandial hr, but its responses were not altered with or without simultaneous administration of cimetidine. These findings indicate that acid hypersecretion in basal and postprandial states after ACT may be attributed to hypergastrinemia and that endogenous acid is capable of releasing secretion but not effective on the release of PP.