Cerebral blood flow and P300, a long-latency, positive component of the scalp-recorded, event-related potential (ERP), were measured in 26 patients with multiple cerebral infarcts (mean age, 65.0 years). Compared with age-matched normal subjects, patients with multiple cerebral infarcts had significantly lower cortical blood flow values and had prolongation of the P300 latency. There was a significant correlation between the P300 latency and the mean cortical blood flow values in patients with multiple cerebral infarcts. These results suggest that, in patients with multiple cerebral infarcts, the cognitive impairment associated with change of the ERP may be related to reduction of cortical blood flow.