Treatment of cancer patients with the antitumor antibiotic bleomycin (BLM) is associated with lung damage which can progress to pulmonary fibrosis. Shortly after intratracheal (it) administration of BLM to experimental animals there is an influx of inflammatory cells into the lung. These inflammatory cells, consisting primarily of polymorphonuclear cells, monocytes and lymphocytes, are believed to modulate the pathogenesis of pulmonary fibrosis. The objective of the present study was to determine the role of specific T-lymphocyte subpopulations in this disease process following a single it administration of BLM to C57BL/6J mice. Specific in vivo T-lymphocyte subpopulation depletion was accomplished by multiple intraperitoneal administrations of cytotoxic monoclonal antibodies to mice prior to and following BLM administration. Acute lung damage was assessed by measuring levels of angiotensin-converting enzyme and total protein in the bronchoalveolar lavage fluid 7 days after BLM treatment while chronic fibrosis was assessed by total lung hydroxyproline 28 days after BLM. Although we were able to deplete lymph nodes and BAL of specific T-lymphocyte subpopulations we were unable to detect a difference in the extent or severity of either the acute or chronic stage of BLM-induced lung damage. These results suggest that BLM lung disease progresses unabated in C57BL/6J mice despite virtually complete depletion of either L3T4+ or Lyt-2+ T-lymphocytes. Although a greater than 80% decrease in Thy-1.2+ T-lymphocytes was accomplished, there was a residual population of Thy-1.2+ lymphocytes resistant to the cytotoxic antibody. It is possible, therefore, that this population of cells does play a role in the development of BLM lung disease.