Isolates of H. pylori from patients with chronic gastritis and peptic ulcer, were found to be capable of inactivating lysozyme and intercide (the bactericidal component of human leukocytic interferon). The expression and penetration capacity of their antilysozyme activity (ALA) and antiintercide activity was determined. The wide spread of ALA among H. pylori clinical isolates associated with inflammatory changes in bioptic specimens, confirmed the leading role of this microorganism in the pathogenesis of the gastric mucosal lesions. The retrospective analysis of clinical cases made it possible to recommend the use of the ALA sign as one of the criteria for choosing the scheme of eradication therapy even at the stage of the initial diagnostics of H. pylori infection.