The aim of the study was to investigate epitope specificity of new monoclonal antibodies (MAb) against human IgG1, IgG2, IgG3, IgG4 and to estimate some models of their application. The topography of subclass- specific epitopes on IgG molecules was investigated using a set of peroxidase-labelled MAb under study and unlabelled MAb with known epitope specificity by means of competitive inhibition test. The scheme of class and subclass-specific IgG epitopes location is presented. Combinations of MAb directed to spatially distant epitopes for two-site immunometric quantification of IgG subclasses were selected. They consisted of pairs of subclass-specific MAb used as capture reagents and complementary enzyme- labelled class-specific developing MAb. Labelled subclass-specific MAb are shown to be suitable also for immunosorbent assay of sub-isotypic patterns of antibody response against foreign and auto-antigens.