De-Nol® (colloidal bismuth subcitrate, CBS) precipitates in an acid environment and adheres to the exudate layer covering an ulcer crater; moreover, CBS blocks pepsin activity, retards hydrogen-ion back-diffusion and stimulates prostaglandin synthesis. The average healing rate in duodenal ulcer (DU) after 4 weeks’ treatment with CBS is 78 % versus 63 % with cimetidine. In a direct comparison, CBS gives 84% healing as opposed to 78 % with ranitidine. The average healing rate after 4 weeks’ treatment with CBS in gastric ulcer (GU) is 68% compared to 54% with cimetidine. The percentage of relapse-free patients, 1 year after DU or GU healing, with CBS is substantially higher than is the case with H2-receptor blockers.