An investigation of 56 children with appendicular peritonitis complicated by multiple-organ failure has revealed typical, in the authors' opinion, metabolic and immunological changes such as the regulation of organism to minimization of the energy exchange with catabolism of the functionally important proteins and the formation of multiple-component secondary immunodeficient state. The data obtained facilitate earlier diagnosis of the multiple-organ failure and optimization of the management which resulted in 2 times less lethality among such patients.