Visual evoked potential determinations and the number connection test were performed for 49 patients with stable chronic liver disease and portal hypertension but without clinical evidence of hepatic encephalopathy. The latencies of the evoked potential components N2, P2 and N3 were significantly prolonged compared to the controls. Seven patients had a prolonged N2, 10 had a prolonged P2, and 14 patients had a prolonged N3 latency. Only five of these patients had increased theta activity of the electroencephalogram. When age norms were applied, the number connection test was significantly prolonged only in the 16-36-years age group. It is concluded that the visual evoked potential identifies a group of patients with neurophysiological abnormalities and may be useful in identifying those at risk of developing overt encephalopathy.