In 14 patients with encephalopathy due to cirrhosis of the liver levels of consciousness were assessed by clinical ratings and continuous reaction time measurements. The observations were compared with similar measurements made in patients with chronic brain syndrome, patients sedated with diazepam, and hospitalized controls. Patients with hepatic encephalopathy were characterized by having slower reaction times than patients from the other groups. Furthermore, the performance of several liver patients was decreasing during the test. This phenomenon was not seen in the other groups. The continuous reaction times in the liver patients were correlated with the clinical ratings, but the reaction times appeared to be more sensitive, since on several occasions this test became abnormal before the clinical rating. Patients dying within 3 months after the test had more abnormal reaction times than patients surviving this period, indicating a relation between this test and the severity of the liver disease.