Event-linked brain potentials were studied in ten essentially healthy volunteers (six men, four women) aged 18-24 years. Subjects were presented with rare deviant and frequent standard visual stimuli in the standard odd-ball paradigm in conditions of active attention to stimulation and in conditions of distracted attention. Differences between deviant stimuli (50, 100, and 150 msec) and standard (200 msec) stimuli ranged from 50 to 150 msec. Negative difference waves (deviant stimulus with distracted attention minus control stimulus of the same duration) were seen at differences of 100 and 150 msec and these were most marked in the right temporal cortex 200-400 msec from stimulus onset. As this wave was seen in conditions of distracted attention, it appears to be a visual analog of mismatch negativity and reflects the process of the automatic detection of stimuli with deviant durations.