Lung irritants contribute towards chronic obstructive lung diseases. Therefore, apart from the technical measures, the workers in the chemical industry who are at risk of inhaling lung irritants enter an occupational medical programme. This includes periodically a lung function test. An analysis performed on 532 such workers suggests that there is no relation between the occupational risk mentioned and the FEV1 of the workers. However, the well known injurious influence of smoking is shown, the reduction of FEV1 in heavy smokers being 4.9% of the standardized values (p less than 0.025). In a previous analysis a reduction of FEV1 greater than expected was observed; this reduction disappeared by means of using other reference values. The EGKS reference values (revised 1983) used now are generally well accepted.