Volatile metabolites present in expired lung air were collected by odor sampling techniques and analyzed by gas chromatography-mass spectrometry. The study population included controls matched for age and smoking history with patients newly diagnosed with lung carcinoma. Significantly greater concentrations of o-toluidine were found in the lung air of patients with lung carcinoma than either age-matched or younger controls. Aniline was present in half of the patient population but absent in age-matched controls.