1. A method of ascertaining the current function or condition of at least one lung of a living subject selected for a lung evaluation, comprising the steps of: measuring a nitrogen monoxide content of expiration air, comparing at least one of the nitrogen monoxide content and a time-distribution of the nitrogen monoxide content of the gas generated in said at least one lung during at least one exhalation phase with at least one of a maximal nitrogen monoxide content and a time-distribution of the maximal nitrogen oxide content of a living subject having an unimpaired lung function, and interpreting a deviation manifested by said comparison as an impaired lung function.