Introduction. Currently, genetically engineered biological drugs (GEBDs) directed against key pathogenetic factors of airway inflammation are included in the treatment strategies for patients with severe bronchial asthma (SBA). One of the most important participants in the development of SBA among blood cells include eosinophils and neutrophils, the decrease of which is one of the markers of the effectiveness of GEBD. However, some GEBDs have been shown to affect monocyte counts and other hematopoietic characteristics. Considering the peculiarities of the course of the disease and the comorbid background of patients of older age groups, the study of age-related characteristics of hematological indices, depending on the chosen therapy tactics and in the context of SBA phenotypes, is an urgent area of modern research. Purpose of the study: to study the age characteristics of hematological indices in the treatment of SBA with GEBD. Materials and methods. A single-center prospective clinical study was conducted, which included 664 patients diagnosed with Asthma J45 who were treated at the Pulmonology Expert Center, established on the basis of the St. Petersburg State Budgetary Healthcare Institution City Multidisciplinary Hospital No. 2 in 2024. The study was performed in two stages: 1st - comparison of hematological indices of patients with SBA receiving basic therapy and patients receiving one of GEBD in addition to basic therapy; 2nd - study of age-related characteristics of hematological indices in patients with SBA who received GEBD, in the context of two disease phenotypes: allergic and non-allergic. Statistical processing was performed using the SPSS Statistics 20.0 application package. Results. The GEBD group showed lower counts of all blood cell populations, with a decrease in the relative eosinophil count (p=0,00652). In the elderly, the number of these cells also decreased, but without a specific decrease in eosinophils (p=0,0601). Among both patients with allergic and non-allergic SBA phenotype, a statistically significant increase in neutrophil count with age was found. Discussion. The decrease in the relative number of eosinophils in the treatment of GEBD is associated with the specific effect of drugs, the absence of this pattern among the elderly may be associated with age-related neuroimmunoendocrine desynchronosis. The age-related increase in neutrophils is probably due to the development of inflamaging in this cohort of patients, which requires further studies. Conclusion. In the group of patients receiving GEBD, a lower number of all considered blood cell populations was detected, with a decrease in the relative number of eosinophils (which was not typical for people of the older age group). An increase in neutrophil count with age was found among both patients with allergic and non-allergic SBA phenotype.