The effects of diazepam and GABA on intestinal motility were investigated in fasted dogs fitted with strain-gauge transducers. Injected intravenously at 9.00 and 16.00 h, diazepam (0.5 mg kg-1) affected intestinal motility only during darkness i.e. from 19.00 to 7.00 h. These jejunal motor effects which were mimicked by GABA, (0.3 mg kg-1 i.v.) corresponded to a disruption of the migrating myoelectric complex (MMC) with an increased contractile activity. These results demonstrate that benzodiazepines affect the intestinal motility in dog and suggest that the effects are related to sleep-stages.