There is an increasing interest in the measurement of nitric oxide (NO.) in the airways. NO. is a free radical that reacts rapidly with reactive oxygen species in aqueous solution to form peroxynitrite which can then break down to nitrite (NO(2)(-)) and nitrate (NO(3)(-)). NO(3)(-) is considered a stable oxidative end product of NO. metabolism. The aim of this study was to assay NO(3)(-) in exhaled breath condensate (EBC) of normal nonsmoking and smoking subjects, asthmatics, patients with obstructive pulmonary disease (COPD), and patients with community-acquired pneumonia (CAP). EBC was collected using a glass condenser and samples were assayed for NO(3)(-) by ion chromatography followed by conductivity measurement. NO(3)(-) was detectable in EBC of all subjects. NO(3)(-) was elevated in smokers [median (range)] [62.5 (9.6-158.0) microM] and in asthmatics [68.0 (25.8-194.6) microM] compared to controls [9.6 (2.6-119.4) microM; p=0.003 and p=0.006, respectively], whereas NO(3)(-) was not elevated in COPD patients [24.1 (1.9-337.0 microM]. The concentration of NO(3)(-) in patients with CAP [243.4 (26.1-584.5) microM] was higher than that in controls (p=0.002) and NO(3)(-) values decreased after treatment and recovery from illness [40.0 (4.1-167.0) microM, p=0.009]. This study shows that NO(3)(-) is detectable in EBC of healthy subjects and it varies in patients with inflammatory airway diseases.