To evaluate chronic loss of lung function in cotton dust-exposed workers, a 5-yr follow-up study was performed in Shanghai, China from 1981 to 1986. Workers at a nearby silk thread manufacturing mill were used as a control population. There were 384 cotton textile workers restudied from an original group of 446, and 403 silk workers restudied from the original 468. The presence of byssinosis among retested cotton workers at the time of first survey was 7.3%. The prevalence of byssinosis was 9.7% at the initial survey among those lost to follow-up. No byssinosis was found among control subjects. The mean annual decline in FEV1 was 39.5 ml among cotton workers and 30.6 ml for silk workers (p < 0.05). The greatest annual decrements were found among smoking cotton workers, but nonsmoking cotton workers also lost lung function at a faster rate than silk nonsmokers (annual loss = 33.3 ml versus 24.4 ml, respectively). Autoregressive modeling revealed that after adjustments for age, sex, height, and smoking, cotton dust exposure was significantly associated with decline in FEV1. Moreover, across-shift drop of 5% or more at the time of first survey was predictive of 5-yr decline in FEV1. Cotton workers who had an acute response (5% or greater drop in FEV1 at the time of first survey) suffered a 57.0 ml/yr FEV1 drop compared with a 35.1-ml drop among cotton workers with less acute response at baseline (p < 0.01). Silk workers with or without 5% across-shift drops had similar annual rates of decline (-33.8 ml and -36.1 ml, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)