Since little is known of the effects of age, gender, and body size on exhaled nitric oxide (NO) production, we have conducted a prospective study to examine these factors in a healthy nonsmoking women (mean age +/- SD 47.7 +/- 15.8, range 20-79 years). Exhaled NO was measured by an automatic chemiluminescence analyzer (Sievers NO Analyser 280) at steady expiration. Men had significantly higher exhaled NO levels than women (p = 0.001). Although exhaled NO levels did not correlate with age (r = 0.12, p = 0.17), it correlated significantly with height (r = 0.23, p = 0.02), weight (r = 0.34, p