A double-blind cross-over study of the antidiarrhoeal effects of loperamide and diphenoxylate in 29 patients with chronic diarrhoea due to intestinal resection is presented. Most of these subjects had had surgery for Crohn's disease which was in a stable and nonactive phase during the study. Loperamide and diphenoxylate were presented as identical capsules. Each was administered for a minimum duration of 25 days. The number of capsules required to control diarrhoea was significantly smaller in the loperamide group than in the diphenoxylate group. Loperamide was also statistically superior to diphenoxylate at reducing the number of stools and improving the faecal consistency. Nineteen of the 29 patients considered loperamide to be the most effective antidiarrhoeal drug, five preferred diphenoxylate and five did not notice any difference.