Immediate-type allergies are frequent in specific occupational environments. Most important is to consider the possibility of occupational factors in allergic diseases. Depending on the substance, immunological and non-immunological mechanisms may be relevant for symptom elicitation. According to European Directive 2001/83/EC, in vivo test allergens are medicinal products, whereas test allergens for in vitro use are medical devices following respective regulations. Standardized test preparations for in vivo and/or in vitro testing for specific IgE to occupational allergen sources are rare. False-negative as well as false-positive test reactions may occur with current test methods for the detection of specific IgE to occupational allergen sources. Compared to ubiquitous inhalant allergens (cut-off ≥3.00 mm wheal diameter), for occupational allergens, a different cut-off (wheal diameter ≥ 1.5 mm) applies. Skin prick testing, intracutaneous testing, and in vitro investigation of specific IgE constitute one component in a stepwise assessment for the diagnosis of allergen-induced occupational diseases. High- and low-molecular-weight allergens have to be considered as occupational allergen sources in specific work environments.