We present a 49-year-old man, in whom chest X-ray showed multiple, ill-defined densities in both lungs. Diagnosis was obtained by means of examination of biopsy specimens from a thoracotomy. By means of immunohistochemical techniques, monoclonal lymphoid cells were demonstrated. This finding is conclusive of a diagnosis of malignant lymphoma. Due to the multiple localizations, surgical extirpation and radiotherapy were not feasible. The patient was given chlorambucil for 5 months, followed by six courses of cyclophosphamide, vincristine and prednisone.