Neutrophils have recently been attracting significant attention, due to appearance of new information on functional heterogeneity of this cell population that significantly determines pathways and features of pathological process. Objective: to determine morphological and functional features of neutrophils and structure of pharyngeal tonsil in children with adenoiditis and otitis media with effusion. Materials and Methods: In 38 children aged 3 to 7 years (25 - with uncomplicated chronic adenoiditis, 13 - with adenoiditis complicated with secretory otitis media) activity of acid and alkaline phosphatases and activity of cationic proteins was determined in peripheral blood neutrophils by cytochemical methods; NBT test was performed. Relative area of follicles, diffuse lymphoid tissue, blood vessels, fibrous tissue, as well as the presence and composition of intraepithelial infiltration, type of surface epithelium was evaluated on histological specimens of biopsies obtained during adenotomy (10 - in patients with uncomplicated chronic adenoiditis, 13 - with chronic adenoiditis complicated with secretory otitis media). Results: Decrease of the relative area of follicles (p = 0.04) as well as decline of the activity of acid phosphatase in the blood neutrophils [0.26 (0.22, 0.32) vs 0.32 (0.28; 0.36); p = 0.03] was observed during complicated course of chronic adenoiditis compared to uncomplicated form of the disease. Activity of oxygen-dependent mechanisms of cytotoxicity of peripheral blood neutrophils, assessed in NBT-test, did not differ between children with complicated and uncomplicated course of chronic adenoiditis. Conclusion: Reduced neutrophil acid phosphatase activity with intact ability to generate reactive oxygen species may be one of the causative factors of chronic adenoiditis, subepithelial morphological rearrangements in lymphoid tissue and development of exudative otitis media.