Objective: to identify the frequency and etiology of latent sensitization among frequently ill preschool children living in Rostov-on-Don.Materials and methods: 40 preschool-age children (5.3±1.2 years old) who are under medical supervision for frequent respiratory diseases of a protracted nature were examined. According to the nature of the clinical course, the following subgroups were identified: 1st subgroup — frequently ill children with recurrent respiratory tract pathology: adenoiditis, bronchoobstructive syndrome (n=19), 2nd subgroup — frequently ill children with different duration of episodes of acute respiratory diseases: from 3 to 5 days and from 5 to 10 days. The mandatory criterion for inclusion in the group was the absence of hereditary burden due to allergic pathology. All patients underwent an allergological examination, including the determination with the help of an automatic immunochemiluminescent analyzer (Immuno CAP 100 Phadia AB, Switzerland) of specific blood IgE to the antigens of Timothy's meadow, rPh1 p1, Phl p 5; antigens of Altenaria alternata, rAlt a1; antigens of ragweed, nAmb a1; to the antigens of wormwood nArt v1.Results: sensitization to the main allergens that are causally significant for the region is formed in 33–74% of cases in frequently ill preschool children living in Rostov-on-Don. The main causally significant allergen, sensitization to which is diagnosed in most of the subjects, is the major fraction of Ragweed Ragweed (nAmb a1). Sensitization to the major fraction of the common Wormwood allergen (nArt v1) is not diagnosed in a monovariant, but always accompanies hypersensitivity to high Ragweed ragweed.Conclusions: the presence of concomitant pathology of the respiratory tract in the form of adenoiditis, bronchoobstructive syndrome, as well as a long (more than 5 days) course of frequently recurrent acute respiratory diseases is a factor indicating a high probability of latent sensitization in frequently ill preschool children, which is formed in 33-74% of cases. It is recommended that frequently ill children with symptoms of recurrent respiratory tract pathology perform allergodiagnostics with the identification of specific IgE to the main causally significant allergens for the region.