About 100 years ago the concept of allergy was introduced and is still valid in consideration of new scientific insights. Due to the different reaction patterns of these allergies, they can be divided into four types. By applying in vivo tests, such as the skin test or provocation test, the sensitization of a person can be determined in the course of immediate hy-persensitivity. The detection of specific IgE plays a prominent role in allergy diagnostics. This is enabled by a variety of immunological and molecular-biological laboratory tech-niques such as RAST and ELISA. In allergy research especially the Western blot is often the method of choice. It provides important information about whether the patient responds with one or several proteins in an allergen extract. In addition, it provides the basis for identification and characterization of new allergens.