Twenty-two patients with active Crohn's disease treated with salazosulfapyridin or prednisone, were in addition given metronidazole 1.000 mg daily or placebo for two months each in a double-blind cross-over study. No statistically significant effect was observed on the overall clinical condition in the 20 patients who completed the trial, although haemoglobin rose and ESR fell significantly in the metronidazole periods. In the 6 patients with colonic involvement only an improvement was registered both in symptoms and laboratory values.