A battery of computer-based psychological tests given to seven patients with chronic hepatic encephalopathy showed them to be intellectually impaired, particularly on speed-based measures, as compared with general hospital patients and with patients with cirrhosis but without clinical or electroencephalographic evidence of encephalopathy. Two of the seven patients in the latter group also showed evidence of cognitive impairment on some tests. The effects of levodopa were also evaluated by sequential assessment with these tests. Although there was some improvement in speed of performance on certain tasks and a suggestion of deterioration on other measures, there was little overall change. It is concluded that levodopa has an 'arousing' or antidepressant action and that its effect on intellectual functions is secondary to this alerting effect and is consequently dependent on the emotional and attentional status of the patient.