Detection of antigen-specific IgG and lymphocyte proliferation test (LPT) are important for the diagnosis of hypersensitivity pneumonitis (HP) as well as for the identification of the inciting antigen. Although a variety of antigens including bacteria, fungi, animal protein, and chemicals can cause HP, there is currently no standardized, internationally accepted immunological test for evaluating exposure to these antigens. Only a few studies demonstrated the clinical utility of specific IgG against bird antigen and Trichosporon asahii; thus, development of standardized tests is needed for future clinical investigation.