An allergic reaction to stings by insects can occur within minutes and may be fatal. The history serves to assess the severity of the reaction and may aid in the identification of the insect involved. The diagnosis is established by a skin test and the hyposensitization tested by determining the levels of insect venom specific IgE. Minor allergic reactions can be treated with drugs, the more severe forms require hyposensitization therapy with pure insect venom, especially when the risk of re-exposure to insect sting is high. By means of the rush-hyposensitization, a protection against insect stings can be achieved within 1 week. With increasing dosage, patients who have previously had severe reactions to insect stings, develop allergic side-effects. During the course of the treatment with insect venom, the levels of allergic IgE- and the levels of the protective IgG-antibiodies rise. After 6 months, the allergic antibody levels fall, the protective IgG-antibodies, however, remain above their pretreatment level.