In 35 newborns and children at the age under 4 mos with Hirschsprung's disease, colonic microflora was studied. Disbacteriosis at phase 1 was revealed in 1 (2.9%) child, at phase 2--in 7 (20%), at phase 3--in 27 (77.1%). In acute form of Hirschsprung's disease, in 68.5% of cases, disbacteriosis at phase 3 with the signs of enterocolitis causing acute ileus was revealed. Intestinal perforation against background of enterocolitis developed in 8 cases.