Objective: To compare and contrast the efficacy and tolerability of a proton pump inhibitor, pantoprazole, to that of an H2 antagonist, ranitidine, in the treatment of patients with mild to severe reflux esophagitis., Background: Reflux esophagitis is a common illness affecting 5-10% of the world's population. Acid reflux plays a major role in the disease's genesis, as do esophageal and gastric motility disturbances., Methods: 315 patients (intent to treat) with endoscopically confirmed reflux esophagitis (Savary-Miller (SM) stages II and III) were recruited to the study by 46 mexican investigators in nine centers. Patients received either pantoprazole 40 mg once daily or ranitidine 150 mg twice daily in this double blind, randomized, parallel group study. Patients not achieving complete endoscopic healing after four weeks of therapy received an additional four weeks of treatment. Drug tolerability was assessed by adverse event reporting during the study., Results: After four weeks pantoprazole therapy, 81% of patients with SM II and 67% of the patients with SM III were healed; in contrast ranitidine healed only 67 and 30% of the patients respectively, all results expressed on an per-protocol basis. After eight weeks therapy the healing rates for pantoprazole group increased to 94% and the ranitidine group to 74% (p = 0.001). The incidence of adverse events was less than 2% in both treatment groups, thus both therapies were found to be well tolerated., Conclusions: Pantoprazole is superior to ranitidine in the treatment of mild to severe reflux esophagitis and is equally well tolerated.