54 patients with acute pneumonia were examined. There were 36 men and 18 women aged 16 to 72 years. Use was made of the clinico-roentgenological, bronchological and laboratory methods including biochemistry and immunoassays to assess the gravity of the patients' condition. The system protease inhibitors, the concentration of immunoglobulins in blood serum, circulating immune complexes, functional activity of neutrophils and monocytes of peripheral blood were under study. The major part of the patients (45 persons) did not develop destructive lesions, in 9 patients, pneumonia was complicated by suppurative-destructive lesions. In both patients' groups, the disease (in 90.3% of cases) ran its course with the signs of active virus infection. The risk factor for the destruction development was the rise of the laboratory gravity index to over 5-6 marks, a tendency towards the decrease of the phagocytic activity of monocytes and immunoglobulin M, the presence of unbalance in the system protease inhibitors at the expense of inadequate reduction of the antiproteolytic potential.