Previously, we reported that repeated subcutaneous administration of bleomycin (BLM) to rabbits produced functional and structural endothelial damage with no evidence of interstitial fibrosis. In the present study, rabbits received intratracheally a single injection of BLM (6 units/kg, n = 6: "low dose" or 11 units/kg, n = 4: "high dose"); 6 additional animals received intratracheally an injection of saline and served as controls. Four weeks after BLM administration, the low-dose group demonstrated significant reduction in the single-pass pulmonary removal of 14C-5-hydroxytryptamine (5-HT) (p less than 0.05; n = 4), whereas 3H-norepinephrine (NE) removal and 3H-benzoyl-phe-ala-pro (BPAP) substrate for lung angiotensin converting enzyme (ACE) metabolism in vivo, as well as lung and serum ACE activity in vitro remained at control levels. No morphologic or biochemical evidence of fibrosis was observed. In contrast, the high-dose BLM group exhibited significant reductions in 14C-5-HT and 3H-NE removal and 3H-BPAP metabolism in vivo, but no significant changes in lung or serum ACE activity in vitro. Furthermore, there was evidence of fibrosis, as revealed by a 59% increase in lung hydroxyproline content and by light microscopic examination of lung tissue. We conclude that intratracheal administration of BLM to rabbits can produce endothelial dysfunction in the presence or absence of interstitial injury.