An affinity chromatography method for preparation of patient-related antigens from commercially available allergen extracts has been investigated. IgG1,2,4 from a patient previously hyposensitized with dog hair and dandruff allergen was bound to protein A-sepharose. Secondly, commercial allergen extract was applied to the immunosorbent, and patient-related antigens were selectively absorbed by the specific antibodies from the patient serum. Finally, immune complexes containing antigen and IgG were eluted. Alternatively, the antigens alone were purified by retaining the IgG on the column by means of a covalent reinforcement of the protein A-IgG-binding. Purified, patient-related antigens were investigated in crossed immunoelectrophoresis and identity to IgG- and IgE-binding antigens (as determined by the CRIE-technique) was suggested. The affinity purified IgG was unaltered with regard to protein A-binding, binding of antigen and affinity for monoclonal antibody to human IgG-subclasses. Further, it was demonstrated that the antigen-binding capacity of IgG in the immune complexes was intact as evidenced by strong affinity to antigens even at low pH. The antigens eluted together with IgG were predominantly found in immune complexes with a molecular weight of greater than 300 kdalton equivalent to 2 or more molecules of IgG. The possibility of employing a similar method with IgE instead of IgG for preparation of patient-related allergens instead of antigens, is discussed.