Circular muscle contractile activity of the antrum and duodenum and gastric emptying of a liquid test meal were investigated in unanesthetized dogs in which the gastroduodenal junction (GDJ) was altered (Heineke-Mikulicz pyloroplasty). After pyloroplasty, antralization (antral-like contractions occurring in the first portion of the duodenum) was observed during the digestive state. Antralization replaced the normal periods of inhibition that separate periods of duodenal contractions during the interdigestive burst. Bethanechol (0.1 mg/kg sc) and metoclopramide (2.0 mg/kg iv) were capable of stimulating interdigestive contractile activity in the altered GDJ. Pentagastrin (1.0 mug/min iv) produced a differential stimulation on the antrum without appreciably affecting duodenal contractile activity. Pyloroplasty also enhanced the emptying of a 300-ml citrate-fat liquid test meal. An intact hypomuscular segment between the antrum and duodenum is important for normal coordinated contractile activity between the antrum and the duodenum and for the normal gastric emptying of liquids.