We investigated the effects of aerosolized endothelin (ET) on pulmonary mechanics of anesthetized spontaneously breathing rats. ET inhalation caused a concentration-dependent increase in pulmonary resistance (RL). In control condition RL was 0.17 +/- 0.04 cmH2O/ml/s (mean +/- SE; n = 6) and increased to 1.45 +/- 0.28 cmH2O/ml/s (p less than 0.05) after ET 4 x 10(-5) M. The pulmonary responses to ET lasted up to 60 minutes. These results suggest a role for endothelin in the regulation of airway smooth muscle tone.