The invention concerns a method for the determination of antigen-specific antibodies of the immunoglobulin G class in the presence of immunoglobulins of the M class in body fluids by incubation with at least two different receptors R.sub.1 and R.sub.2 and optionally additional receptors, an essential component of R.sub.2 being a binding partner in monomeric form, a reagent for determining an antigen-specific antibody of the immunoglobulin G class as well as the use of binding partners in monomeric form for the determination of an antigen-specific antibody of the immunoglobulin G class.