Nitric oxide (NO) appears to play an important role in the pathophysiology of airway diseases as suggested from measurements of NO in exhaled air, animal and in vitro experiments. As NO is produced in variable amounts within the bronchial system and the nose, we studied the relationship between nasal and bronchial production of NO in patients with asthma and determined to which extent these productions were increased compared to healthy subjects. The nasal and bronchial production rates of NO as a function of breathholding time were assessed in 10 healthy subjects, 7 patients with asthma without inhaled corticosteroids, and 5 patients with asthma and a therapy of inhaled corticosteroids. After a breathhold of 10 s bronchial NO concentrations were elevated in the patients with asthma without steroids by the factor 3.5 (p < 0.005) and nasal concentrations by the factor 1.2 (n.s.) compared to healthy subjects. NO concentrations increased with time. Correspondingly, bronchial production rates were increased by factor 2.7 (p < 0.01) and nasal production rates by factor 1.1 (n.s.) in asthmatic compared to healthy subjects. The asthmatic patients with steroids showed lower production rates than those without steroids. We conclude from these data that in patients with asthma as compared to normal subjects bronchial production of NO is markedly increased, whereas the corresponding relative increase in nasal production is lower.