We isolated the allergenic components of Dermatophagoides farinae (D. farinae) body extracts and determined the frequencies and specificities of IgE, IgG, and IgG4 antibodies binding to components of D. farinae extracts by use of immunoblot technique. A total of 29 IgE-binding components of D. farinae extracts were identified and distributed over the molecular weight range of 13 to 140 kilodaltons (kD). Each component had 3% to 73% frequencies of recognition by individual patient serum, and the major antigenicity of D. farinae was considered to exist in components of 13 to 16 kD, 25 to 30 kD, and 43 to 60 kD. These observations suggested that antigenicity of D. farinae is not restricted to one major allergen, but several components account for the total allergenic activity of D. farinae. We could also demonstrate 27 IgG-binding components of D. farinae antigen. Their frequencies and strength of binding were similar to IgE. IgG4 antibodies in patients with bronchial asthma bound to components with molecular weights 13, 25, 43, and 50 kD had relatively low frequencies of binding to IgE antibodies.