A randomized study was performed in order to compare the course of hepatic encephalopathy in patients treated with neomycin plus magnesium sulfate or with lactulose. Admission criteria were: morphological diagnosis of cirrhosis and absence of comorbidity, of contraindications to drugs, or of previous treatments which could influence the outcome. The treatment groups were similar in terms of clinical characteristics, fatalities, recovery rate from grade 1 encephalopathy, and disappearance rate of neuropsychiatric signs. Transitions from severe to grade 1 or 0 encephalopathy showed a 0.17 (NS) difference in favor of neomycin. Early therapy and evidence of precipitating factors showed a favorable prognostic significance. Ascites, hyperbilirubinemia, poor nutritional state, and hypoprothrombinemia showed bad prognostic significance. This is the first large-scale investigation on hepatic encephalopathy. It demonstrated a similar effectiveness of the two drugs in grade 1 encephalopathy and provides a basis for drug selection in the current management of the syndrome.