In an eight-week double-blind trial, the effectiveness of cimetidine (1.6 g/day) was compared to placebo in 34 patients with symptomatic esophagitis confirmed by endoscopy with biopsies and/or by acid infusion test. Patients treated with cimetidine had significantly less symptomatic days during the first six weeks and less symptomatic nights during the first two weeks, and they consumed less antacids during the whole trial period. Endoscopic evaluation of 17 patients on cimetidine and of 15 patients on placebo did not show any significant difference in severity and extent of esophageal lesions after eight weeks, but histological assessment of 16 patients on cimetidine and 13 patients on placebo showed a significant improvement after eight weeks of cimetidine (P < 0.025). These results show that cimetidine has a rapid effect on symptoms of reflux esophagitis and that, in some cases, it may reduce the esophageal lesions after eight weeks.