Immediate allergic reaction of the skin, non allergic airway responsiveness of the bronchi, and serum IgE levels were estimated in 25 atopic non asthmatic subjects and 15 controls. A good correlation was observed between these three parameters i.e. patients with positive skin response to allergen had increased airway responsiveness and significantly increased levels of serum IgE. However, the serum levels of IgE provided a significantly better indication of the likely presence of bronchial allergic reactivity than did the skin reactivity. The results indicate that knowledge of the airway responsiveness to histamine, skin sensitivity to allergen and serum IgE levels can predict the presence of airways responsiveness to an allergen. In all atopic non asthmatic individuals with a significant correlation between these parameters, the relevant allergen could stand identified as having the potential to provoke attacks of clinical asthma.