Thirty-eight patients with a perennial allergic rhinitis, who developed a nasal response to ingestion challenge with certain foods, were randomly selected for protection tests with oral cromolyn sodium (Nalcrom). The food challenges were performed in combination with rhinomanometry. The patients were pretreated with cromolyn or placebo by double-blind crossover schedule, in a daily oral dose of 200 mg (four times), starting 3 days before and continuing up to 3 days after the food ingestion challenge. The 38 patients previously developed 25 immediate, 24 late, and 6 delayed nasal responses to food ingestion challenge. Cromolyn fully prevented 15, significantly decreased 9, and was ineffective in 1 case of immediate nasal response. Of the 24 cases of late response, cromolyn fully prevented 10, significantly decreased 12, and was ineffective in 2. Of the 6 cases of delayed response, 2 cases were decreased significantly by cromolyn, while the other 4 cases were not. The protection effects of oral cromolyn were highly significant for the immediate and late nasal responses and nonsignificant for delayed responses. It can be concluded that cromolyn in a daily oral dose of 200 mg four times prevented the immediate and late nasal responses to ingested food.