Treatment of duodenitis with cimetidine: a clinical, endoscopic, and histologic study. We studied the effectiveness of cimetidine in the treatment of endoscopically diagnosed duodenitis. Sixty-nine patients with the solitary endoscopic finding of duodenitis (6% of 1,200 patients who underwent fiberoptic endoscopy of the upper gastrointestinal tract in our unit over 3 years) were studied retrospectively: a good clinical response was apparent in 45 of 69 patients treated with cimetidine (65%), and a fair response in another four (6%). In a controlled, randomized prospective study, we evaluated the effectiveness of cimetidine in duodenitis. Statistically significant improvement for the clinical and endoscopic scores was found in 10 patients treated with cimetidine (p less than 0.01). Improvement in the histologic score did not reach statistical significance. No such improvement was demonstrated in seven placebo-treated patients. We believe that duodenitis is a "peptic syndrome," has a good response to cimetidine treatment, and behaves much like duodenal ulcer disease. 