In a double-blind study involving 172 patients, the author investigated the effect of sulfhydryl-containing agents (cysteine and methylmethionine sulfonium chloride [MMSC]) on hematemesis resulting from erosive gastritis induced by nonsteroidal anti-inflammatory drugs. The 56 patients who received cysteine (200 mg orally four times a day) and the 59 patients who received MMSC (500 mg orally four times a day) were significantly (p < 0.01) more hemodynamically stable, with no rebleeding, than the 57 patients who made up a control group. Endoscopy carried out 48 hours after admission demonstrated that gastric erosions were still present in a significantly (p < 0.01) higher number of patients in the control group (20 [35%]) than in patients receiving cysteine (6 [11%]) and in patients receiving MMSC (7 [12%]). Eighteen patients (32%) in the control group required blood transfusion because of continued bleeding or rebleeding compared with only 3 patients (5%) receiving cysteine and 2 patients (3%) receiving MMSC (p < 0.01). Emergency surgery was necessary in 13 patients (23%) in the control group and in 1 patient (2%) in the group receiving cysteine who had rebleeding. Four patients in the control group died postoperatively. The results show that sulfhydryl-containing agents stimulate the healing of erosive gastritis induced by nonsteroidal anti-inflammatory drugs and protect against the complications of bleeding produced by the gastritis.