Antemortem diagnosis of diffuse myelomatous pulmonary infiltrate is rare. We present one such case in which diagnosis was established from bronchoalveolar lavage (BAL) fluid demonstrating the presence of monoclonal plasma cells. The diffuse involvement of the lungs by myeloma was confirmed at autopsy. The possibility of myelomatous pulmonary infiltrates was suggested by the absence of fever or failure to respond to antibiotics but regression with myeloma treatment. Analysis of BAL fluid for the presence of plasma cells and for cytoplasmic immunoglobulin DNA provides a noninvasive means of establishing the diagnosis. Diffuse parenchymal lesions in the lung due to myeloma should be entertained as a differential of pulmonary infiltrates.