The clinical evaluation of newly developed asthma in an adult should alwaysinclude consideration of his occupational environment, since an abundance of different exposures, whichare known causes of asthma, occur in workplaces. Two types of occupational asthma (OA) are distinguished,by whether they appear after a latency period: 1)Immunological OA, characterised by a latency period,caused by high and low-molecular-weight agents, with or without an IgE mechanism 2) Non-immunological,i.e. irritant induced asthma. The first step of the clinical evaluation is to confirm a diagnosis ofasthma. Second step is to find out if there is a temporo-spatial distribution of symptoms and lung functionthat are indicative of OA. Third step is to determine if the disease at hand is an IgE or a non-IgE mediateddisease. Last step is a challenge test that can be either unspecific, in order to assess the responsivenessof the lung, or specific challenge test, especially for the non-IgE mediated OA. The depth of clinicalevaluation may vary from a situation in which a classical history confirms the clinical symptoms in e.g.a baker with confirmed allergy towards well-known allergens and a characteristic pattern in serial measurementsof lung function, to more elaborate investigations in a situation with no or unknown allergen. In thelatter situation, a specific challenge test might be necessary in order to find the offending agent.Finally, challenge tests are important in order to distinguish a causal relation from unspecific hyperresponsivenessin persons with pre-existing asthma. In these situations, extended sick leave and challenge tests canbe the only way to find the answer.