The physiologic way of responding to allergens in healthy subjects is not fully understood, nor the immunopathological mechanism in patients with allergies. Despite the accepted theory of Th1-type immune response in healthy subjects that should result in the formation of "blocking antibodies" and thus the absence of a clinical symptoms of allergic disease, no such increase was observed during the natural exposure of the Ambrosia elatior plant pollen. For one immunoglobulin class (sIgG2) slight fall in serum levels was shown, which could, theoretically, play a role in neutralizing the circulating allergen. The characteristics of humoral immunity in people with allergic diseases during the natural exposure of the pollen of the Ambrosia elatior plant is not only an increase in sIgE levels but also increase in some other classes and subclasses, traditionaly classified as Th1 immunoglobulin (A1, G3, G4). The results of this study show that the natural exposure of allergic persons to the environmental allergen has the similar effect on increase of sIgG4 in allergic persons comparable to those in hyposensitisation. Therefore, the rise of IgG4 is probably not by itself a mechanism that leads to clinical improvement in hyposenzitized patients. That argument, together with the high level of allergen-specific serum sIgM levels and also other imunoglobuline classes, dispute against the "theory of blocking antibodies". The results obtained could be used for further research in patients with allergy, primarily the investigation of total barrier function, dynamics of immunoglobulin classes and subclasses in other body specimens (nose and mucous membrane biopsies), determination of blood allergen levels and determination of sIgE using this quantitative method, possible differences in sIgM and other sIg levels in patients with anaphyllaxis, potential therapeutic application of sIgG2 antibodies as well as research in immune cells and their mediators. That way, a more complete insight about immune events in healthy people and patients with allergies could be obtained.