Proteolytic systems of tissue and blood plasma take part in the processes of adaptation and protection of an organism, as well as in development of pathological reactions. We have studied the activity of kallikrein, kallikreinogen, angiotensine transforming enzyme, α1-protease inhibitor, and α2-macroglobulin in healthy children in different age periods, in newborns with hypoxic-ischemic encephalopathy, in children with infectious-inflammatory diseases of the urinary system, obesity, and metabolic syndrome.The activity of the kallikrein-kinin system was increased in all the groups against the background of the decreased inhibitory activity of blood plasma of different intensity, which can be used for the prediction of the course of diseases.