The number and types of mononuclear cells obtained by bronchoalveolar lavage from 105 marrow transplant patients with and without cytomegalovirus pneumonia were studied to determine whether: (1) CMV pneumonia was associated with local recruitment of lymphocytes and lymphocytes of particular subtypes to the lung, and (2) whether local recruitment was affected by the known risk factors for the development of CMV pneumonia, namely acute graft-versus-host disease and total body irradiation. Results showed a significant increase in the