All employees from Norwegian cement plants, are invited to participate. The workers will perform spirometry, single-breath determination of carbon monoxide uptake, blood samples before and after a working shift of 6-8 hours, and again after 24 hours. Information on respiratory symptoms, allergy and former respiratory disease as well as exposure information will be given on a self-reported questionnaire. Changes in lung function indices, nitric oxide levels and serum inflammatory markers will be calculated. Nitric oxide will only be measured in non-smokers. We will compare cement dust exposed workers with low-level or non-exposed workers (controls).