(1) A new series of anti-allergic drugs (AH 6556, AH 7079 and AH 7725) were shown to inhibit immediate-type allergy. They act by inhibiting release of pharmacological mediators, and they do not possess any bronchodilator activity. (2) Inhibition of allergic reactions was shown experimentally in a wide range of in vitro test models, and supports the findings in the preliminary in vivo studies in experimental animals. (2) The experimental evidence suggests that these compounds have some qualitative and quantitative advantages over disodium cromoglycate.