A study was carried out to assess the effectiveness of ranitidine in the short-term treatment of reflux oesophagitis. In a double-blind randomized trial of 37 outpatients with symptomatic, endoscopically proven, moderate or severe reflux oesophagitis, 18 patients received ranitidine (150 mg twice a day) and 19 patients received identical-looking placebo tablets for a period of six weeks. Clinical, laboratory, and endoscopic assessments were made initially, and at the end of six weeks. Two patients withdrew during the trial. Endoscopic evidence of improvement was found in 15 of 17 ranitidine-treated and in five of 18 placebo-treated patients. This difference was significant (P less than 0.01). Antacid consumption was significantly lower in the ranitidine-treated group (P less than 0.01). Improvement in histological findings, and the relief of retrosternal pain, regurgitation, dysphagia, and epigastric pain did not achieve levels of statistical significance. No adverse clinical or laboratory changes occurred in patients in either group. It is concluded that, as judged by endoscopic evidence, ranitidine is an effective drug for the short-term treatment of reflux oesophagitis.