A relationship between enteric microbiocenosis and severity of type 1 diabetes mellitus was detected. Microbiological analysis showed II-IV degree dysbacteriosis in all diabetic children. Long-term therapy with probiotics aimed at eradication of opportunistic microflora resulted in recovery of microbiocenosis, which was paralleled by improvement of the clinical status, regression of complications in children who were ill for a long time, and prevention of complications in children with newly detected diabetes. These results indicate the leading role of chronic enteric toxic infectious process in the development of complications of type 1 diabetes. The significance of infection in the pathogenesis of other noninfectious diseases in man is discussed.