Psychotropic action of a branched-chain-enriched amino acid solution (Aminoleban) was quantitatively and visually examined in six cirrhotic patients with mild hepatic encephalopathy (grades I and II) using electrophysiological and psychometric methods. Neurophysiological effects of the amino acid solution were observed by comparing topographic spectrum analyses of electroencephalography (EEG) before and immediately after an intravenous 3 h infusion of the solution. The delta wave in the frontal region diminished from 61 +/- 13 to 12 +/- 4% (P < 0.01) and the alpha wave in the occipital region increased from 11 +/- 3 to 51 +/- 11% (P < 0.01). Latencies of the P3 wave in visual evoked potentials, which were topographically recorded in the occipital region, shortened from 220 +/- 32 to 148 +/- 19 ms (P < 0.01). Latencies of the P300 wave in event-related potentials, which were topographically recorded in the centro-temporal region, shortened from 493 +/- 81 to 360 +/- 93 ms (P < 0.05). Topographic reaction pattern of P300 was irregular toward the occipital or parietal region in cirrhotic patients. The EEG frequency power spectrum, illustrated by the colour density spectral array of computer-aided polysomnography analysis, clearly showed a gradual increase of the alpha wave spectrum and a gradual decrease of the delta wave spectrum after initiation of the infusion. These immediate neurophysiological changes were confirmed by improvement of quantitative psychometric tests including number connection test, reaction time to sound, and digit symbol and block design tests of Wechsler Adult Intelligence Scale.(ABSTRACT TRUNCATED AT 250 WORDS)