Twenty patients with active Crohn's disease, the majority refractory to conventional therapy, were treated with rifampicin, ethambutol, isoniazid, and pyrazinamide or clofazamine for 9 months. After this period, 10 were in remission (Crohn's disease activity index less than 150). Of the 10 not in remission, three had been at 6 months, but had relapsed on treatment. Nine of 10 patients on steroids at the beginning were off steroids at 9 months. Six patients came to surgery during the period, five for stricture formation without evidence of florid Crohn's disease outside the strictured segment. Three young patients with severe Crohn's disease facing total colectomy were spared surgery. No serious drug-related side-effects were encountered. The results of this pilot study suggest that controlled trials of antimycobacterial chemotherapy, using four or more of the best agents available, are worthy of assessment in Crohn's disease.