This paper describes the effects of repeated exposure to gasoline and ethanol exhaust fumes on the pulmonary mechanics of rats assessed by whole-body plethysmography. Two groups of 12 male Wistar albino rats each were tested before and after exposure to diluted gasoline or ethanol exhaust gases for 5 weeks, 8 h per day and 5 days per week. An additional group of 12 rats were exposed to clean air under the same experimental conditions. The variations of the functional parameters observed in the three groups before and after exposure were compared. Peak Expiratory Flow and Forced Expiratory Mean Flows in the ranges 0-25%, 25-50% and 50-75% of Forced Vital Capacity were significantly reduced in animals exposed to gasoline exhaust fumes, whereas the group exposed to ethanol exhaust fumes did not differ from the control group. This respiratory impairment is probably due to the presence of SO2 and the quality of the hydrocarbons in gasoline exhaust gases.