SUMMARY One hundred patients with benign gastric ulceration were treated in a single-blind, endoscopically controlled trial to assess the relative efficacy of cimetidine (1 g daily) and Caved-S (six tablets daily). Ulcer healing was assessed after six weeks' treatment, and, if incomplete, after a further six weeks. There was no significant difference between the two drug regimens (approximately 63% at six weeks and 91% at 12 weeks). If an ulcer remains unhealed after 12 weeks' treatment the patient should undergo surgery. There was no difference in the relief of day pain between the two drug regimens but cimetidine was more effective over the first two weeks of treatment in relieving night pain, than was Caved-S (p<002). After ulcer healing, drug dosage was reduced (cimetidine to 400 mg at night and Caved-S to two tablets twice daily). So far, 56 patients, 28 in each group, have completed the first year's maintenance treatment, and there have been four ulcer recurrences in each group (14%).Carbenoxolone until comparatively recently was the drug of choice for the treatment of gastric ulceration.' In 1978 we published the results of a study2 in which patients under the age of 60 years were treated with either cimetidine or carbenoxolone and those over 60 with cimetidine or Caved-S. Cimetidine was found to be more effective than carbenoxolone. The healing rates for Caved-S and cimetidine were similar. Caved-S contains deglycyrrhizinated liquorice and thus has none of the potential side-effects of carbenoxolone3 (fluid retention, congestive heart failure, hypokalaemia, and hypertension).Following this study, we decided that, before Caved-S could be unreservedly recommended for the treatment of gastric ulceration, a further trial was required, this time incorporating larger treatment groups and patients of all ages. The results of this trial form the basis of this paper.