A multidisciplinary approach to diagnosis is a widely accepted principle in modern medicine. Most physicians and pathologists in particular adhere to this tenet and apply it to their daily practices. It may be fair to say that in any perusal of pathology reports generated at most US institutions, a good number of them would include phrases or sentences such as "clinical correlation recommended" or "this diagnosis cannot be made on histopathologic grounds alone, further interpretation is needed in light of clinical and radiographic findings." Although pleas have been made in the past to bring clinicians and pathologists together, (1) it is still unusual to see "clinical papers" in a pathology journal or to read a pure pathology article in a clinical journal. Hypersensitivity pneumonitis (HSP) is a multifaceted respiratory disease that may mimic almost any interstitial lung disease, some pulmonary infections, some cases of bronchiolar disease, and even cases of diffuse fibrosing diseases of the lung. (2-5) Initially recognized only in farmers and pigeon breeders, HSP is now known to represent a rather broad group of complex, immunologically mediated lung disorders brought about by exposure to a variety of environmental, occupational, and recreational agents, resulting in a wide variety and sometimes substantial numbers of affected individuals, that is, workers in the textile and automotive industries. (6-12) Because of its clinical complexity, broadening spectrum of affected individuals, and still incompletely understood pathogenesis, HSP is particularly suitable for discussion using the previously cited multidisciplinary approach to diagnosis of pulmonary disease. This special section in this issue of the ARCHIVES addresses clinical, histopathologic, and immunologic aspects of HSP. The special section is made up of 4 separate articles: my commentary and perspectives offered by 3 experienced physicians--a pulmonologist, a histopathologist, and an immunologist. Recognizing that HSP is clinically challenging, Dr Madison notes the disease can be quite variable in its clinical presentation, severity, and natural history and calls attention to the importance of considering HSP in the differential diagnosis of patients with interstitial lung disease because HSP is often treatable through avoidance of exposure to relevant antigen(s). The important question of whether a lung biopsy is needed for diagnosis is also explored by Dr Madison in his clinical article. In that regard he states: "When a clinical history identifies an offending antigen, positive precipitins are identified, and clinical and radiographic findings are consistent with HSP without suggesting another disease process, many clinicians would agree that invasive procedures are not always necessary." However, when the clinical presentation is not typical and serologies, chest imaging studies, and inhalation challenges are not conclusive and the diagnosis still remains uncertain, lung biopsy will be indicated. To me, this is encouraging as it means that, at least for the time being, pathologists will continue to play a role in the diagnosis of this intriguing disease.