Gastrointestinal myoelectric activity was studied in 3 conscious fasted dogs with electrodes surgically implanted in the stomach and small intestine, during separate and combined i.v. infusions of 13-norleucine motilin (13-nle-motilin) and pentagastrin (PG). Basal recording confirmed the presence of regular interdigestive myoelectric complexes (MC). 13-Nle-motilin infusion below 50 ng/kg per h was without effect: higher doses up to 400 ng/kg per h resulted in interpolation of one or more MC in the spontaneous sequence. The rate of aboral transit of 13-nle-motilin-induced MC did not differ significantly from that of spontaneous MC. When MC were abolished by feeding or PG infusion, simultaneous 13-nle-motilin administration was without effect on spike activity, but slightly attenuated the accelerating effect of gastrin on the gastric pacemaker frequency. The myoelectric events triggered by 13-nle-motilin suggest that in the conscious dog the polypeptide may not act directly on the smooth muscle cell, as it does in vitro, but through an extra-enteric neural control mechanism which is uncoupled by gastrin.