The goal of this study is to appreciate the early and late sequelae caused by Chlorine Gas. 186 exposed patients have been admitted to our unit since 1962-119 had functional respiratory explorations (FRE) with an analysis of blood gases, 79 underwent a study of carbon monoxide transfer. The results are in accordance with the literature for example 25% of the CO transfer test were pathological. 56 occupationally exposed subjects having had at least three acute episodes of exposure have been compared to 197 control subjects (groups were classed in function of age, tobacco intake, and pulmonary antecedent). Chlorine exposure even when frequent has no the influence on the FRE results or the appearance of pulmonary pathology. The pre-existence of a pulmonary disease doesn't affect the prognosis.