Provocation tests with allergens play a critical role in differential diagnosis of allergic diseases. The nasal allergen provocation test and the conjunctival allergen provocation test are particularly useful in the diagnosis of allergies with the underlying mechanism involving IgE-dependent reactions. Interestingly, the symptoms typical of both the nasal allergen provocation test and conjunctival allergen provocation test occur during the tests: ocular symptoms during the nasal test and typical nasal symptoms during the conjunctival test. These symptoms provide a picture of the early and late phases of the allergic reaction. Increasing attention is given to the role of the two provocation tests in differential diagnosis of food allergies, and the first studies involving food challenge tests provide a solid foundation for further research in this area.