Despite experimental evidence for an increase in extravascular lung water (EVLW) after inhalation injury, thermal-dye estimations of EVLW, extravascular thermal volume (EVTV), have repeatedly failed to demonstrate its presence in patients. This situation was evaluated in a sheep model. Under halothane anesthesia one lung was insufflated with cotton smoke and the other with air. EVTV values were 8.4 +/- 0.48 ml/kg at base line and were not elevated at 24 h after smoke inhalation (8.3 +/- 0.45 ml/kg; means +/- SE). Gravimetric analysis 24 h after smoke inhalation showed the development of edema in smoke-exposed lungs. The blood-free wet weight-to-dry weight ratio of the smoke-exposed lungs (5.4 +/- 0.32) was significantly higher compared with the contralateral unsmoked lungs (4.3 +/- 0.15; P less than or equal to 0.05). The thermal-dye technique thus underestimates EVLW. Poor perfusion of the smoke-exposed lungs 24 h after injury was demonstrated indirectly by killing a group of sheep with T-61, an agent that causes a dark red coloration of well-perfused lung areas, as well as directly by measurement of blood flow utilizing a radiolabeled microsphere technique. Thus the inability of the thermal-dye technique to detect the lung edema may be the result of poor perfusion of the injured lung.