Pulmonary function tests are tools available to the researcher and clinician to evaluate the ability of the lung to perform its essential function of gas exchange. To meet this principal function, the lung needs to operate efficiently with minimal mechanical work as well as provide an optimally minimal barrier to diffusion. Tests of lung function permit the nondestructive assessment of a continuum of lung performance, a continuum that may be influenced temporarily or permanently by inflammatory events or structural alterations. In theory, any function test conducted in human subjects can be applied to animals and largely interpreted in the same manner. Fortunately, those physiologic principles that form the basis for clinical assessments of function seem to apply to animals in a quantitative as well as qualitative manner. Nevertheless, being aware of the species differences and technical pitfalls is critical to the ultimate interpretation of the tests, especially when comparing them to their human analogues in health and disease. The test described in the paper will be useful to OAQPS and ECAO as a resource tool for analyzing toxicological data from animals for use in regulatory procedures.