The aim of our investigation was to determine the state of anti-endotoxin (AET) immunity in patients with moderate and severe persistent bronchial asthma. 109 patients were examined receiving outpatient treatment of the basic disease. All patients were divided into two groups: group 1 — patients with moderate bronchial asthma — 68 subjects (62,4%) with average score of 3.00 ±0.14 according to ACQ, FEV₁ — 67.01 ± 2.10 %; group 2 — patients with severe bronchial asthma — 41 subjects (37,6 %) with average score of 4.06 ± 0.12 according to ACQ, FEV₁ — 34.45 ± 1.05 %. It was proved that in both clinical groups the levels of total secretory IgA and secretory AET-lgA in induced sputum were higher than those of healthy donors. It was observed the increase of the level of AET-IgM in blood serum in both clinical groups in comparison with donors, as for the level of serum AET-IgG patients of the studied groups were treated as normal responders. It was registered the increased level of AET-lgA in blood serum in group 1, in group 2 this indicator was getting closer to that of the donors. The increased level of C-reactive protein was determined in both groups. It is assumed that the imbalance of anti-endotoxin immunity influences the severity and the course of bronchial asthma according to the phenomenon of endotoxin aggression.