ABSTRACT. A patient with multiple myeloma had pancytopenia after treatment with melphalan and prednisone and died of an interstitial pneumonia. Post‐mortem examinations showed cytomegalic cells in the lungs. Lung tissue showed a high titer of cytomegalovirus. Only when other causes have been ruled out by microbiologic, serologic, and histologic examinations should melphalan be believed to cause respiratory illness.