The aim of the present study was to elucidate the risk factors that could delay gastric ulcer healing when either a proton pump inhibitor or an H2-receptor antagonist is used for gastric ulcer treatment. Endoscopically-diagnosed gastric ulcer patients (216 men and 96 women, mean age: 57+/-13 years) were investigated. All patients were consecutively recruited and randomly assigned to receive H2-receptor antagonist (n = 196) or proton pump inhibitor (n = 116) treatment for eight weeks. Chi-squared tests and multivariate analysis to determine factors influencing ulcer healing were used to analyse the patients profiles, endoscopic findings, and Helicobacter pylori-infection status. In the H2-receptor antagonist group, the most important risk factor was a large ulcer size (> 2 cm diam.), followed by a linear shape of the ulcer, undermining tendency of ulcer, previous history of gastric ulcer, and H. pylori infection. In the proton pump inhibitor group, linear shape of the ulcer was the only significant risk factor for slow ulcer healing; other factors, including H. pylori infection, were insignificant. These results indicate that ulcer morphology may be the most important information for predicting ulcer healing, and that H. pylori infection does not delay gastric ulcer healing when proton pump inhibitor treatment is used.