The group 2 allergens of Dermatophagoides pteronyssinus (Der p) and Dermatophagoides farinae (Der f) are the major source of allergens for patients allergic to house dust mites (HDMs). Previous studies have reported the existence of several polymorphic residues of Der p 2 and Der f 2. In this study, recombinant group 2 allergens of Der p (rDer p 2) and Der f (rDer f 2) were produced in E. coli from the major isoforms of each cDNA, in order to evaluate their usefulness for the detection and standardization of allergens, and for the immunotherapy of patients allergic to HDMs in Korea. cDNAs of the major isoforms of Der p 2 and Der f 2 were prepared from HDMs found in -Korean houses. The IgE-binding activities of the prepared rDer p 2 and rDer f 2 were analyzed using a Western blot immunodetection system and ELISA in the pooled sera of 10 patients allergic to HDM. Both rDer p 2 and rDer f 2 bound to IgE in the pooled sera, and their activities were comparable to that of Der p 2 in HDMs. The rDer p 2-specific IgE level was higher than the rDer f 2-specific IgE level in patients' sera. The specificity of the monoclonal antibodies raised against both isoforms was analyzed by ELISA and immunogenicities of the antibodies were evaluated. Two out of four clones of rDer p 2-specific mouse monoclonal antibodies (IgG) reacted with both rDer p 2 and rDer f 2, whereas the other two did not react with rDer f 2. rDer f 2-specific monoclonal antibody reacted with both rDer f 2 and rDer p 2. The cross-reactivity of rDer p 2 and rDer f 2-specific monoclonal antibodies with both recombinant allergens indicates that epitopes responding to these antibodies are present. rDer p 2 and rDer f 2 may be useful for the detection and standardization of group 2 allergens of HDM and for the diagnosis and immunotherapy of patients allergic to HDM in Korea.