A formal single-blind multicentre study has been set up to investigate the probable benefit of combined therapy of the cytoprotective agent De-Nol (colloidal bismuth subcitrate, CBS) and an acid-suppressing drug (cimetidine) in the treatment of duodenal ulcer. The protocol compares the therapeutic benefit of CBS alone and cimetidine alone with CBS + cimetidine, the treatment period being 28 or 56 days. Patients whose ulcers heal within the therapeutic phase will be followed up until relapse or 12 months, whichever is the longer. The paper presented reports interim results from this trial. Comments and clinical observations on the probable value of this combined treatment and the selection of patients suitable for such treatment are discussed.