In the present study the prophylactic effect of concentrated wheat fibre on duodenal ulcer recurrence was evaluated. Eleven grams of fibre (Fiberform) or placebo was added to an ordinary Norwegian diet for 1 year after endoscopic healing of duodenal ulcer. The ulcer recurrence rates were 84% (31 of 37 patients) in the fibre-supplemented group and 85% (30 of 36 patients) in the placebo group (NS). The effect on ulcer symptoms was similar in both groups. Side effects were infrequently seen. A concentrated wheat fibre supplement seems to have no preventive effect when given to duodenal ulcer patients living on a traditional Norwegian diet.