A simple technic for studying the pulmonary mechanics of rats by whole body plethysmography is presented. The parameters measured were: Tidal Volume (TV); Respiratory Frequency (RF); Transpulmonary Basal Pressure (TBP); Dynamic Compliance (Cdyn); Functional Residual Capacity (FRC); Transpulmonary Pressure/Volume curve (TP/V); Forced Expiratory Volume of 1/4 second (FEV 1/4); Expiratory Reserve Volume (ERV); Inspiratory Capacity (IC); Inspiratory Reserve Volume (IRV); Forced Vital Capacity (FVC); Residual Volume (RV); Forced Expiratory Mean Flow between 100-50% (FEMF 100-50), 50-25% (FEMF 50-25) and 25-0% (FEMF 25-0) of the FVC, and Total Lung Capacity (TLC). In order to verify the accuracy of the technic, common male adult Wistar rats, in which pulmonary obstructive disease is normally expected, were first submitted to these functional tests and then to pathological examination. According to the intensity of the morphological pulmonary lesion, the rats were divided in two groups: with and without suppurative pneumopathy. The analysis of the pulmonary function data showed significant decrease of the FEV 1/4 and FEMF 50-25 and increase of the FRC and RV in the groups with pulmonary suppuration. Thus, a discriminant function could be established to characterize the two groups with 100% efficiency. It was concluded that these pulmonary function tests are a valuable and reliable tool to detect lung diseases in rats.