To clarify the relative timing of clinical changes in duodenal motility and pancreatic secretion in newborn calves, we recorded duodenal electrical and mechanical activity and analysed pancreatic secretion and migrating myoelectric complex (MMC). In eight calves integrated recordings were derived from sites near the duodenal bulb and pancreatic accessory duct orifice, and pancreatic juice was sampled after an overnight fast, after a feed, and during reversible cold vagal blockade. Peak secretion coincided with duodenal irregular spiking activity and the nadir with absence of spiking. Feeding elicited electrical and mechanical hyperactivity in the duodenum, dissipated the MMC temporarily, and dramatically increased the juice volume and bicarbonate and protein outputs. Periodic fluctuations in secretion started shortly after a feed, as did recovery of the duodenal myoelectric complexes. Cold vagal blockade reversibly disrupted the synchronous changes in duodenal motility and pancreatic secretory activity, though the close association was not totally obliterated. In milk-fed calves interdigestive pancreatic secretion apparently rises and falls in phase with migrating myoelectric complexes of the proximal duodenum and the vagus is largely, though not exclusively, responsible for co-ordinating these changes.