Nineteen MDI exposed workers showed ventilatory changes, after eight hour exposure, mainly involving upper respiratory airways; the changes reversed following a bronchodilator aerosol. An incomplete recovery of VC was found in some subjects; therefore, the possibility of changes in the lung elastic recoil forces was hypothesized. No statistically significant differences were found as to occupation and smoking habit, which suggests that even low MDI concentrations could be enough to give rise to acute effects. The greater impairment found in subjects who were already affected by morning time emphasizes the necessity that such subjects were not employed in their specific work.