Lactitol is a disaccharide analogue of lactulose which is available as a pure crystalline powder. The efficacy of lactitol in the treatment of chronic hepatic encephalopathy was assessed in 9 cirrhotic patients in a randomised, double-blind, cross-over comparison with lactulose. The sugars were dispensed in solutions, identical in taste and appearance and with similar physico-chemical properties, which contained either 66.7 g/100 ml of lactitol or 66.7 ml (44.5 g)/100 ml of lactulose syrup. Patients were treated for periods of 3 months with each sugar, during which time they were monitored frequently by use of a number of clinical, psychometric and laboratory variables. The sugar solutions were dispensed in an initial dose of 0.75 ml/kg which was adjusted, as necessary, in order to produce two semi-soft stools per day. An adequate catharsis was achieved with a mean (+/- 1 SD) equivalent daily dose of 31.9 +/- 11.2 g of lactitol or 32.9 +/- 16.7 ml (21.9 +/- 11.1 g) of lactulose syrup. Both sugars were equally as effective in the treatment of this condition, even though events likely to cause decompensation arose in 5 patients during treatment with lactitol but in only 1 during treatment with lactulose. Side effects appeared to be more frequent during treatment with lactulose, despite the fact that the parent sugar was diluted in the trial solution; thus 5 patients experienced excessive flatulence and 8 experienced diarrhoea on lactulose compared with only 2 and 4 on lactitol, respectively. In all cases the excessive flatulence occurred independently of sugar dosage whereas the development of diarrhoea was dose-related.(ABSTRACT TRUNCATED AT 250 WORDS)