Occupational or professional asthma is defined as adult asthma, i.e., an inflammatory respiratory disease characterized by the presence of variable airflow limitation or bronchial hyperreactivity secondary to conditions and causes associated with a given occupational or working environment - not with stimuli found outside the workplace. Depending on the physiopathological mechanism involved, a distinction is made between immune asthma (with or without IgE mediation) and non-immune asthma. It is difficult to establish the relationship among the symptoms of asthma, the patient's professional activity and the presence or absence of sensitization to certain agents in the working environment. Guided compilation of the case history and measurement of nonspecific bronchial hyperreactivity and bronchial inflammation are currently essential in the diagnostic approach to occupational asthma. Whenever possible, allergists should establish the cause-effect relationship in occupational asthma, as required by the medical-legal and social implications of the disease. Occupational asthma remains a minority diagnosis among occupational diseases in general. Adequate personnel training and the creation of diagnostic centers may help to ensure correct and rapid detection of this disease.