Plasma fibronectin (FBN) and angiotensin I-converting enzyme (ACE) were prospectively measured in 50 burn patients from the day of admission to day 28 after the trauma with the aim of finding biochemical markers of pulmonary injury by smoke inhalation. Patients were divided into three groups on the basis of fiberoptic bronchoscopy results (group I: healthy lungs; group II: burned lungs; group III: infected lungs). A decrease in FBN concentrations was observed in the three groups but was larger in group II than in the other groups, especially at day 2 (P < 0.05). A similar profile was observed for plasma ACE activity. Factors other than lung injury may influence plasma FBN and ACE levels, in particular the burned body surface area, an acute event such as septicemia, or outcome. However, repeated measurements of both markers could help in the assessment of lung injury in the follow-up of burn patients.