The nasal concentration of nitric oxide (NO) was measured by chemiluminescence in healthy volunteers 3-68 years of age, and in patients suffering from common cold and chronic sinusitis. The concentration of NO in healthy subjects, 233.2 +/- 66.8 ppb (mean +/- SD), was found to be relatively independent of age and body size. The measured levels of NO did not differ between healthy volunteers and common cold patients, but they were significantly lower in patients suffering from chronic sinusitis, 96.4 +/- 72.8 ppb. As NO is a regulator of mucociliary activity and has bacteriostatic and antiviral effects, the decreased concentration of NO in patients suffering from sinusitis suggests that lack of NO may contribute to the pathogenesis of this disease. The importance of NO for the mucociliary system was emphasized by the finding that the 2 patients with the lowest nasal concentration of NO were found to manifest functional and morphological changes of the mucociliary system that are typical of acquired mucociliary dysfunction.