The extended use of intradermal allergy tests underlines the importance of factors which may modify the skin reaction. During routine allergological examination of patients suffering from asthma, symptomatic treatment is often necessary in order to keep the patient fit for the procedure, and in some instances corticosteroids are unavoidable at the time of testing. Thus the question arises if these drugs may interfere with the immediate skin wheal reaction and cause falsely negative results.Inconclusive findings are reported (7, 8) concerning the delayed type of allergic skin reactions, e.g. the tuberculin test, when this is carried out during ACTH or steroid treatment.Several authors state, however, that the immediate skin wheal reaction is not significantly altered by ACTH or corticosteroids in therapeutic doses (3,4, 8) and a corresponding view IS expressed without any reservation in a recent textbook of allergology (2).Applying intradermal allergy tests as a screening examination in a great number of asthmatic patients, we have a vague impression that giving steroids may, after all, lead to falsely negative reactions in some instances. Therefore this prospective study has been carried out in order to test the general validity of the statement mentioned above.