Occupational asthma is the occupational respiratory disease most frequently recognized by the CSST. Sixty new cases are compensated annually, half of which are in young workers. In some industrial sectors, fewer than five years elapse between the start of exposure and the appearance of the first symptoms. To have a better understanding of this phenomenon, the researchers will evaluate instruments for measuring immunological and functional parameters for monitoring occupational asthma on three cohorts of workers. The targeted sectors are those where flour, laboratory animals and latex are found, which are among the main causal agents of Québec cases of occupational asthma. From this study, it will be possible to determine the incidence of specific immunological sensitization, of respiratory symptoms or occupational rhinoconjunctivitis, of bronchial hyperreactivity and occupational asthma in these groups at risk. Its results will promote better prevention of occupational asthma and its long-term sequellae, while increasing scientific knowledge about its natural history.