We investigated whether the mismatch negativity (MMN) of the auditory event-related potentials can be elicited on the basis of implicit knowledge and what the effect of explicit knowledge compared to implicit knowledge is on deviant detection. We recorded the MMN to occasional changes in the pitch relation of tone-pairs roving on different pitch levels. The experiment consisted of a video watching block, an attend block and again a video watching block interleaved with interviews to determine whether the subjects possessed implicit or explicit knowledge of the deviants. Our results confirmed that the MMN can be elicited in subjects that have implicit knowledge only. The MMN of subjects with explicit knowledge was, however, larger compared to subjects with implicit knowledge only. Explicit knowledge compared to implicit knowledge lowered the RT and gave rise to a P3 that was absent in subjects with implicit knowledge. The results indicate that implicit knowledge is sufficient for MMN elicitation but that explicit knowledge to some degree can affect the change detection processed underlying the MMN as well as the subsequent target detection processes.