One fifth of adult-onset asthma cases are associated with adverse effects occurring at work. In investigating occupational asthma an overall assessment is required of materials handled by the patient at work. This evaluation is based on several sources: history of exposure from the patient, medical records in the occupational health service, process, material and chemical data obtained from the workplace, including safety data, and if necessary, workplace measurements and other documents. In suspected occupational asthma, the occupational health service has the primary responsibility to carry out assessment of exposure. In order to start investigations of occupational disease without delay, it is essential to recognize the role of work in the pathogenesis of the disease.