Nitric oxide (NO) is commonly thought to reveal more precise values of pulmonary gas uptake through alveolar-capillary membranes (DL) than the normally used carbon monoxide (CO). Since such measurements are influenced by a significant endogenous NO delivery within human airways, we propose the use of the naturally occurring (15)N-labelled stable nitric oxide isotope (15)NO. It occurs with a relative abundance of 0.37% of the dominating isotope (14)NO. Therefore, the endogenous (15)NO production can be neglected. In the present pilot study we demonstrate the workability of (15)NO in determining DL in healthy individuals. In seven female and 15 male volunteers, averaged values of DL increase with increasing mean alveolar volume as well as individual body height ( P=0.000001). Due to the very high significance level obtained from the multiple regression analysis, we conclude that the application of (15)NO establishes a novel approach to calculate standard values of DL. Such calculations can be employed to predict a reference for patients who suffer from pulmonary diffusion limitation.