This report describes the development of a new panel of monoclonal antibodies established after immunization of mice with purified surfactant protein D of the rat. To enhance the detection of SP-D in formalin- or Schaffer-fixed samples, immunohistochemistry was performed by using microwave pretreatment of paraffin sections. Using these new antibodies that bind to type II epithelial cells, Clara cells, and alveolar macrophages, the responses of lung parenchymal cells were examined in a radiation-induced fibrosis model. Increased accumulation of extracellular SP-D in the alveolar space was found. Double staining with anti-surfactant protein A antibodies revealed different Clara cell populations containing one or both types of surfactant proteins.