The present thesis explores the relationship between occupational rhinitis and occupational asthma under the postulates of the "united airways disease" concept that refers to the multiple links observed between rhinitis and asthma. Accordingly, the main objective of this thesis is to demonstrate the concomitant expression of significant changes in nasal patency and bronchial calibre following exposure to occupational agents during specific inhalation challenges, complementing the assessment with the investigation of changes in markers of airways inflammation in nasal lavage. To achieve the objectives, we set up a protocol to diagnose occupational rhinitis and conducted a study from January 2005 to January 2007 at Hopital du Sacre-Coeur de Montreal in subjects undergoing investigation for occupational asthma. The reliability of the main research tools---acoustic rhinometry and nasal lavage---used to investigate occupational rhinitis was tested by analyzing the reproducibility of the methods. Both methods proved sufficiently reproducible to be included in our investigative protocol. The results presented in this thesis demonstrate a joint reaction of the nose and the lungs in a group of study subjects after performing specific inhalation challenge. This supports the concept of a "united airways disease" and its applicability to rhinitis and asthma of occupational origin. However, the results also show that although occupational rhinitis frequently coexists with occupational asthma it can also be present without occupational asthma. The assessment of upper airways inflammation in a subgroup of study subjects by the nasal lavage method allows us to observe significant changes in eosinophils counts after the challenge that correlates with the decrease in nasal patency observed in the same subjects.

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