Several studies have stressed the role of food intolerance as one of the major factors in the pathogenesis of irritable bowel syndrome (IBS). The purpose of this study was to determine the proportion of patients with IBS that can respond well to an exclusion diet with/without oral disodium cromoglycate and to document the effects of this combination. We selected 120 ambulatory patients with diarrhoeic type IBS; 66 of them (55%) had a concomitant food intolerance (assessed by skin prick test), showing a positive reaction to one (32%) or more foods (68%). Sixty-three (52.5%) tested by cytotoxic test showed more positive reactions. The results were evaluated by means of semiquantitative subjective and objective scores. Thirty patients were randomly treated with a strict exclusion diet, while the other 36 were treated with both exclusion diet and oral disodium cromoglycate (250 mg four times daily) for four months. We observed an improvement of symptoms in 18 (60%) of the 30 patients that had received the only exclusion diet, whereas thirty-two of 36 patients (89%) who had undergone both dietary and cromoglycate treatments showed an improvement that was clinically and statistically significant (p = 0.01).Thus it is concluded that dietary exclusion in association with disodium cromoglycate is most effective in carefully selected patients with diarrhoeic type IBS, with a very high probability of prolonged symptomatic benefit in those subjects that do respond.