We report a correlation between P300 and cerebral blood flow in 11 patients with chronic moderate alcoholism. The patients had been drinking more than 83 ml pure alcohol equivalent everyday for more than 10 years and did not have any other neurological diseases. The P300 latency was significantly longer in the chronic alcoholism group than in the age-matched healthy control group. There was a significant negative correlation between the P300 latency and the thalamus blood flow in the chronic alcoholism group. These findings suggest that there is a subclinical disturbance of cognitive function in chronic alcoholism and that the prolongation of P300 latency is related to the decrease in thalamus blood flow in chronic alcoholism.