Occupational asthma and allergic diseases of the upper airway play an important role in occupational diseases. The most frequent allergens, which causes occupational respiratory diseases in the Czech Republic, are isocyanates and wheat and rye flour. Isocyanates are the substances used in car industry during production of polyurethanes, they are in colours and glues. Occupational allergic asthma and rhinitis are diagnosed using specific challenge tests with substances from the workplace. These tests can be done in a special exposure box in a lab with substances taken by hygiene specialists from the patient´s workplace or using direct exposure at the workplace. Spirometry and anterior active rhinomanometry are used as objective methods during these tests. For prognosis the early diagnosis and withdrawal from the occupational allergen exposure are essential. Keywords: allergic asthma, allergic rhinitis, irritant-induced asthma, irritant-induced rhinitis, isocyanate, occupational disease, specific inhalation challenge.