An immunoperoxidase method of detecting respiratory syncytial virus antigens in paraffin sections of pneumonic bovine lung. 
Using an avidin-biotin-peroxidase complex immunoperoxidase staining method, respiratory syncytial virus (RSV) antigen was demonstrated in glutaraldehyde-fixed, paraffin-processed lung sections from calves with induced RSV pneumonia.  The virus also was detected in formalin-fixed, paraffin-processed lung sections from calves with naturally occurring RSV pneumonia.  Specific immunoperoxidase staining was detected within the cytoplasm of epithelial cells and syncytia in small bronchi, bronchioli, and alveoli.  Staining also was detected within exudates in airway lumina and in mononuclear and multinucleate cells within alveolar lumina.  Optimal intensity of staining was achieved by proteolytic enzyme treatment of lung sections, using 0.1% pronase and overnight incubation in diluted primary antiserum.  The distribution of antigen had a close correlation with presence of lesions.  Antigen-staining patterns were similar in lung tissue from calves with naturally occurring and induced RSV disease.