[Atopy: definition--pathogenesis].

After a short historical review about the detection of reagins by Coca and Prausnitz-Küstner 1921-1923 and about their physico-chemical characterisation as IgE-antibodies by Ishizaka and Johansson 1967-1968 the definition and the clinical relevance of atopy is discussed. The IgE-regulation by interleukins and the pathomechanism of IgE-mediated allergies is reviewed. Of special importance is the IgE-mediated inflammatory late-reaction and the--therefore caused--unspecific hyperreactivity of the stricken tissue, both characteristic features of asthma bronchiale as well as atopic dermatitis.