Responses of the gastric antrum and duodenum to some drugs were studies in fasted state of conscious dogs using implanted force transducer and/or electrodes. Continuous i.v. infusion of pentagastrin (12-30 micrograms/kg-hr), secretin (1.8 u/kg-hr) and atropine (30-120 micrograms/kg-hr) suppressed the development of the interdigestive myoelectric complex or the interdigestive contractions. During infusion of atropine or secretin, action potentials superimposed on basic electric rhythm (BER) and contractions were frequently observed in the duodenum in spite of motor quiescence in the antrum. A bolus i.v. injection of bethanechol (10-20 micrograms/kg) clearly produced action potentials and contractions in the duodenum, while, in the antrum, only a few contractions were observed. Pentagastrin (12-30 micrograms/kg-hr, 5-10 micrograms/kg i.v.) induced weak but high-frequency contractions in the antrum, whereas, in the duodenum, contractions were scarcely observed except the case of the infusion of the drug over 30 min. The drug also changed the frequency and amplitude of BER remarkably in both regions. Phentolamine (3.0-6.0 mg/kg-hr, 1.0-1.5 mg/kg i.v.) introduced strong contractions similar to the interdigestive contractions. The result indicates that diminution of the adrenergic nerve activity of the myenteric plexus is one of the factors participating in occurrence of the interdigestive contractions.