During the last year exhaled nitric oxide (NO) has been proposed as a marker of airway inflammation. More knowledge of the production and transfer of this molecule are needed in order for NO analysis to become a clinical tool. This was the aim of the study. Exhaled NO values from multiple flow rates were used to model alveolar NO, transfer rate and tissue concentration of NO in the airways. Three flows rates, 0.005, 0.1 and 0.51 sec(-1) were found to be optimal. The NO transfer rate of the airways was 9 +/- 2 ml sec(-1), the tissue source was 75 +/- 28 ppb and the alveolar fraction of NO was 2 +/- 1 ppb in 10 healthy subjects (mean +/- CI95%). In conclusion, we have shown that it is possible to get more information about the distribution of NO in the lungs and the airways than only a single value from one expiratory flow rate can give. Further studies will reveal if this airway modelling can be useful in disease of the respiratory system.