This review deals with the diagnostics of immunoglobulin defects. The development of methods used to detect and quantitate concentrations of immunoglobulins and their subclasses was shortly discussed; following by the role of antibodies in the host defence. Seven out of the ten main immunodeficiencies with the prevalence of antibody defects were then delineated. The diagnostics of humoral immunodeficiencies was illustrated by the example of three boys with hypogammaglobulinemia and three children with common variable immunodeficiency. Percentages of B lymphocytes varied, independent with the very decreased concentrations of immunoglobulin. Concentrations of IgG, IgA, IgM, IgE and IgG subclasses in healthy children of ages from birth to 16 years, were presented in the tables.