SummaryPulmonary clearance of Staphylococcus aureus and plasma angiotensin-converting enzyme (ACE) activity were investigated in an experimental mouse model of kerosene aspiration. Twenty-four hours after acute kerosene aspiration, mice were exposed for 30 min to an aerosol containing the pathogen, and the uncleared bacteria ratio (UBR) determined 4 h after nebulization. The results showed a significant increase (P = 0.004) in UBR in animals with severe pneumonitis (0.44 + 0.05) when compared with controls (0.24 + 0.03). This impairment in lung clearance correlated with the increase in lung weight and the decrease in plasma ACE levels. Mice with kerosene pneumonitis had zones of lung injury, and areas with no gross signs of tissue damage. Lung clearance of S. aureus was significantly impaired in damaged areas whereas it was no different from controls in the non-affected areas. It is suggested that the measurement of plasma ACE activity may be an adjunct in the assessment of the extent of lung injury in hydrocarbon aspiration in children.