In guinea pigs, anaesthetised with urethane, stimulation of the peripheral cut end of the cervical vagus activates cholinergic excitatory and non-adrenergic inhibitory fibres to the gallbladder. Central vagal stimulation reflexly contracts the gallbladder by an efferent pathway in the vagus and also activates an adrenergic, non-vagal inhibitory pathway to the gallbladder. Injections of pentagastrin (12–33 μg kg-1 s.c.) or secretin (0.1–0.2 U kg-1 i.a.), doses which produce no effect on gallbladder tone when administered alone, significantly increase the contractions evoked by vagal stimulation.