We studied event-related potentials (ERPs) occurring in response to attended and unattended stimuli in 31 patients with multiple lacunar infarcts. ERPs were recorded during the performance of visual discrimination tasks using three kinds of stimuli. Each component of P300 response to infrequent nontarget stimuli and P300 response to infrequent target stimuli was defined as non-target P3 or target P3. The non-target P3 latency in patients with multiple lacunar infarcts was significantly longer than in 15 age-equivalent normal subjects, while no significant differences could be found in target P3 latency between patients and normal subjects. From the controlled/automatic standpoint these results suggest that multiple lacunar infarcts are related to impairment of automatic processing reflected by non-target P3, although controlled processing reflected by target P3, is less impaired.