Lung function measurements (FEV1/FVC) were made in 700 cotton and 344 manmade fibre workers (mean age 39.0 and 37.1 years respectively). Percentage of the predicted FEV1 (PPFEV1) and FVC (PPFVC) were calculated using regression equations. Mean PPFEV1 did not differ significantly between fibre groups. Mean PPFVC (SD) was significantly greater in cotton workers (97.8(16.4)) than manmade fibre workers (95.3(14.6)), p<0.02. The mean PPFEV1 was significantly lower in current smokers; (n=548) 89.3 (17.8) in comparison to current non smokers; (n=496) 93.1 (16.8), p<0.001. Logistic regression identified smoking (pack years), increasing age, male sex, current cotton exposure and time spent working in the waste room as predictor variables for a lowering of PPFEV1 and PPFVC. Working with manmade fibre lowered PPFVC more significantly than cotton.