An aged beef cow was presented for signs of thoracic disease. A complete cl
inical and diagnostic workup suggested neoplasia. Postmortem examination re
vealed a lymphoma of T-cell lineage confined solely to the thoracic cavity,
predominantly in lung tissue. The diagnosis was based on light and electro
n microscopy, immunohistochemistry, and negative bovine leukemia virus and
bovine immunodeficiency virus results.