20 patients with Crohn's disease took part in a controlled trial in which remission was maintained by either an unrefined carbohydrate fibre rich diet or a diet which excluded specific foods to which a patient was intolerant. 7 out of the 10 patients on the exclusion diet remained in remission for 6 months compared with none out of the 10 on an unrefined carbohydrate fibre rich diet (p less than 0.05, Fisher's exact test). In an uncontrolled study an exclusion diet allowed 51 out of 77 patients to remain well on the diet alone for periods of up to 51 months, and with an average annual relapse rate of less than 10%.