The study demonstrated that lactusan (lactulose) could be used as an effective remedy in dysbacteriosis. Twenty four sick children aged 1 month to 15 years were examined. Administration of lactusan to 21 patients resulted in perceptible improvement of clinical symptoms, mainly to the cessation of diarrhea. In 14 children an increase in the population level of bifidobacteria and lactic acid bacteria and a decrease in the number of opportunistic microorganisms were observed. Lactulose should be referred to prebiotics.