We performed serial pulmonary function measurements in 28 patients with thermal injury in order to investigate the pulmonary effects of smoke inhalation, small and large surface burns, and the combination of burn and inhalation. Patients were studied at postinjury time intervals of 9.0 +/- 0.6 (M +/- SEM), 22.0 +/- 1.6, 37.3 +/- 2.2, 58.4 +/- 2.5 hours; 11.5 +/- 0.6 days; 1.1 +/- 0.1 and 5.0 +/- 0.5 months. Spirometry was found to be as useful as more sophisticated measurements in the examination of both burn and smoke inhalation groups. Smoke inhalation caused severe airway obstruction 9 h after exposure. Patients with surface burn resuscitated with 4 ml of Ringer's lactate/per cent surface area burn/kilogram developed a significant restrictive defect over the first 58 h, despite normal pulmonary capillary wedge pressures. The restrictive defect in these patients correlated with the size of surface and chest burn, degree of fluid retention, and reduction in colloid osmotic pressure. Surface burn and smoke inhalation caused the greatest deterioration in pulmonary function. These defects gradually resolved during the period of observation.