To determine the prevalence of food allergy as a cause of exacerbation of asthma, we studied 300 consecutive patients with asthma (7 months to 80 years of age) who attended a respiratory clinic. Each patient was screened for possible food allergy by means of a questionnaire and by skin prick tests with the six food allergens most common in our area. Patients with either a suggestive history and/or a positive prick test and/or RAST underwent double-blind food challenge with lyophilized food in capsules or food mixed in a broth to disguise its taste. Pulmonary function tests and symptoms were followed for 8 hours after each challenge. Of the 300 patients screened, only 25 had either a history or skin prick tests or RAST responses suggestive of food allergy. Twenty patients had interpretable food challenges. In these 20 patients, food challenge caused asthma in six and caused other symptoms (atopic dermatitis and gastrointestinal symptoms) in five. On rechallenge after pretreatment with disodium cromoglycate (300 mg 30 minutes before the food challenge), the asthmatic response was blocked in four of five subjects. The patients with asthma with food allergy were generally young, had a current or past history of atopic dermatitis, and high total serum IgE levels. Our findings confirm that food allergy can elicit asthma, but its incidence is low, even in the population attending a specialty clinic. Food elimination diets should not be prescribed for all patients reporting an adverse reaction to foods or having a positive skin prick test and/or RAST with food allergens. In patients with asthma caused by food allergy, disodium cromoglycate may be used to complement elimination diets.