A cross-sectional study investigated whether the exposure of sewer workers to hydrogen sulfide (H2S) was associated with reduced lung function. Sixty-eight sewer workers and 60 water treatment workers performed spirometric tests. Job titles were used to classify the sewer workers according to presumed H2S exposure, and water treatment workers served as a comparison population presumed to have no occupational exposure to H2S. There was a statistically significant difference in mean FEV1/FVC values between sewer and water treatment workers of similar age, height, race, and smoking habits (-3.1, s.e. = 1.4). This deficit was greatest (-5.7, s.e. = 2.0) for sewer workers presumed to have high H2S exposure. Nonsmoking sewer workers presumed to have high H2S exposure achieved only 89% of their predicted FEV1/FVC value, whereas nonsmoking water treatment workers achieved nearly 98% of their predicted FEV1/FVC value. In conclusion, this study found evidence that chronic low level exposure to H2S may be associated with reduced lung function.