Mismatch negativity (MMN), observed in event-related potentials (ERPs), constitutes a measurable change in electrophysiological brain activity occurring after exposure to a novel stimulus. In humans, MMN is considered to be related to stimulus discrimination at the cortical level. ERP recording in dogs may present an opportunity to increase understanding of cognitive processes without reliance on observable behaviour, which may be confounded by motivation or training. Preliminary data are presented suggesting the existence of MMN, recorded using a minimally-invasive procedure equivalent to that used in humans, in unrestrained, unanaesthetised dogs. This is the first example of this ERP component in dogs and the method has substantial utility for future research exploring auditory, olfactory, and visual discrimination tasks, development, and breed differences.