The effects of inhalation injury on the pulmonary microvascular fluid flux and bronchial blood flow were examined in a long-term study of sheep (N= 13). They were insufflated with either 48 breaths of cotton smoke (n= 8) or air (n= 5) while they were deeply anesthetized with halothane. After injury, anesthesia was discontinued and the animals were mechanically ventilated throughout the experimental period (24 hours). Bronchial blood flow increased significantly at all time points recorded and reached its peak 20 minutes after the inhalation trauma (11 ± 1 ml/hr to 106 ± 18 ml/hr;p< 0.05). Thereafter, bronchial blood flow decreased to a value that was six to eight times above the baseline measurement for the remainder of the study period. With these changes in blood flow, there was a concomitant increase in lung lymph flow. This variable gradually increased and was 633% of the baseline value (6 ± 1 ml/hr to 44 ± 8 ml/hr) 24 hours after the challenge with smoke. The control animals showed little or no change in cardiopulmonary function during the experimental period. There is no correlation between the increase in bronchial blood flow and lung lymph flow patterns after cotton smoke inhalation injury.