This study employed a cholecystokinin (CCK) antagonist to evaluate whether endogenous CCK regulates fasted and fed motor patterns of the small intestine. Experiments were performed in six conscious dogs, each in duplicate. Motor activity was recorded by six strain-gauge transducers implanted along the small intestine. The effects of the CCK analogue caerulein and the CCK antagonist loxiglumide were studied in fasted and fed states. Computer analysis determined contractile frequency and area under contractions. Caerulein given as an intravenous bolus 30 min after phase III dose dependently caused a burst of phasic contractions preceded by a retrograde giant contraction. Continuous intravenous infusion of 10 mg.kg-1.h-1 loxiglumide completely abolished the effects of 10 ng/kg caerulein, which increases plasma CCK immunoreactivity to postprandial levels. Loxiglumide, at 10 mg.kg-1.h-1, markedly reduced the increase in phasic contractions due to a supraphysiological dose of 50 ng/kg caerulein to 14 +/- 6(SD)% of the control without loxiglumide (P less than 0.01). The motor activity stimulated by the cholinesterase inhibitor neostigmine (10 micrograms/kg) was not altered by loxiglumide. Loxiglumide given in the fasted state decreased contractile frequency from 9.5 +/- 0.7 to 8.1 +/- 0.6/min and reduced the area under contractions during phase II to 81 +/- 5% of the control without loxiglumide (P less than 0.05). Loxiglumide also decreased contractile frequency during the fed state from 9.7 +/- 0.6 to 8.3 +/- 0.5/min and reduced the area under contractions to 78 +/- 6% of the control without loxiglumide (P less than 0.05). Thus loxiglumide acts as a specific antagonist of the actions of CCK on small intestinal motor activity in the dog. Loxiglumide, at a dose that abolishes actions of endogenous CCK, significantly decreased fasting motor activity during phase II. Loxiglumide also significantly reduced motor responses to feeding but did not prevent interruption of migrating motor complex cycle by a meal. CCK plays a physiological role in regulation of fasting and fed motor activity of small intestine, although other factors in addition to CCK mediate meal-induced motor activity.