Nonsteroidal anti-inflammatory drugs and certain food or drug additives are known to induce acute bronchospasms, angioneurotic edema, and urticaria in susceptible patients. Thirty-four patients (17 with asthma and 17 with urticaria), whose case history suggested such intolerance, were challenged orally with increasing doses of seven compounds: acetylsalicylic acid, glafenine, sodium benzoate, sulfur dioxide, potassium sorbate, sodium glutamate, and tartrazine. Among 162 oral provocation tests, 38 were positive (20% decrease in peak flow rate or appearance of acute urticaria/angioneurotic edema). Twenty-four of the 34 patients (nine with asthma and 15 with urticaria) were intolerant to at least one compound. However, no serious reaction was observed. In 20 of these 24 patients (six with asthma and 14 with urticaria), a diet free of additives and nonsteroidal anti-inflammatory drugs resulted, within 5 days, in a marked improvement of symptoms, which persisted 8 to 14 mo after starting the diet. Age, prevalence of IgE-mediated allergy, and nasal polyposis were similar in patients with or without reactions of intolerance. Under the conditions used, oral provocation tests proved to be feasible, safe, and useful in many patients not helped by existing methods.