One hundred and fifty-two patients with endoscopically verified erosive and/or ulcerative esophagitis entered a double-blind, randomized study comparing 20 mg omeprazole given once daily and ranitidine 150 mg twice daily. The efficacy and safety of 4 to 8 weeks' treatment were studied. Macroscopic healing of esophagitis was defined as complete epithelialization of all esophageal erosive and/or ulcerative lesions. One hundred and forty-four patients completed the first 4 weeks of treatment in accordance with the protocol. The healing rate was 67% in the omeprazole group and 31% in the ranitidine group (p less than 0.0001). The corresponding figures after 8 weeks' treatment were 85% and 50%, respectively (p less than 0.0001). The higher healing rate for omeprazole was also accompanied by a significantly faster and more substantial improvement in reflux symptoms. In the patient's own overall evaluation of symptoms, these had resolved in 51% of the omeprazole-treated patients already at the end of the 1st week of treatment, compared with 27% of those given ranitidine (p = 0.009). Both omeprazole and ranitidine were well tolerated, and there were no adverse events or clinically significant changes in the laboratory values attributable to the trial medication.