The prevalence of atopy was evaluated in two groups of subjects with hypersensitivity to nonsteroidal anti-inflammatory drugs (NSAID): 1) 78 patients with aspirin-induced asthma (AIA) confirmed by oral or bronchial provocation challenges 2) 42 subjects with hypersensitivity to pyrazolone drugs (case history and positive skin tests to noramidopyrine/aminophenazone) who tolerated aspirin well. Fifty sex- and age-matched persons from an unselected general population, with no hypersensitivity to NSAID, formed the control group. Atopy was estimated from the results of the following clinical and biologic parameters: 1) personal and family history of atopic diseases 2) skin prick tests with 16 aeroallergens 3) serum levels of specific IgE to five aeroallergens 4) total serum IgE level. Different definitions of atopy were used, consisting of constellations of two or three of the above-mentioned features. The results of the study revealed that the prevalence of atopy varied according to the criteria used for its definition. Irrespective of the definition used, a similar distribution of atopy was observed in both groups of patients with hypersensitivity to NSAID. Atopy was more frequent in either group of patients with intolerance of NSAID than in the control group. Thus, atopy is related to adverse drug reactions to NSAID.