An analysis of clinico-electrophysiological data obtained from 300 patients suffering from focal and croupous pneumonia with nervous system involvement is presented. Clinical syndromes of the nervous system involvement in acute pneumonias are specified. In 7 lethal cases pathomorphological examinations of the brain were carried out. It has been shown that certain complexes of structural and functional non-inflammatory changes in the central nervous system underlie the neurological symptoms. The leading manifestations were: acute progressing dyscirculatory syndrome with impairment of the vascular tone and permeability, dyscirculatory hypoxia and intoxication accompanied with edema of the brain and the pia; dystrophic changes in the neurons, glia and myelin.