A commercially available antigen assay (Pastorex Aspergillus) was used to detect Aspergillus antigen in serial bronchoalveolar lavage (BAL) fluids and sera of patients undergoing bone marrow transplantation (six patients with autopsyproven aspergillosis and 10 control patients without evidence of fungal infection). Aspergillus antigen was not detected in 17 BAL fluids of the six patients with proven aspergillosis. In two of the six patients the assay gave positive results in serum specimens. Three of the 10 control patients showed reactive BAL fluids. It is concluded that the latex agglutination assay of BAL fluids has no value in the diagnosis of invasive (pulmonary) aspergillosis in patients undergoing bone marrow transplantation.