AIM: Helicobacter pylori(Hpylori) has been linked to chronic gastritis, peptic ulcers, gastric cancer and MALT-lymphoma.Conventional invasive tests are less sensitive than noninvasive tests in diagnosing H pylori infection in patients with bleeding peptic ulcers. Polymerase chain reaction is a sensitive and accurate method for diagnosing H pylori infection. The aim of this study was to evaluate the diagnostic role of mucosal polymerase chain reaction for H pylori infection in patients with bleeding peptic ulcers.METHODS: In patients with bleeding, non-bleeding peptic ulcers and chronic gastritis, we checked rapid urease test,histology, bacterial culture and mucosal polymerase chain reaction for detecting H pylori infection. Positive H pylori infection was defined as positive culture or both a positive histology and a positive rapid urease test. For mucosal polymerase chain reaction of Hpylori, we checked vacA (s1a, s1b, s1c, s2, m1, m1T, m2),iceA1,iceA2 and cag A.RESULTS: Between October 2000 and April 2002, 88 patients with bleeding peptic ulcers (males/females: 60/28, gastric ulcers/duodenal ulcers: 55/33), 81 patients with non-bleeding peptic ulcers (males/females: 54/27, gastric ulcers/duodenal ulcers: 45/36) and 37 patients with chronic gastritis (males/females: 24/13) were enrolled in this study. In patients with bleeding peptic ulcers, non-bleeding peptic ulcers and chronic gastritis, 45 patients (51%), 71 patients (88%)and 20 patients (54%) respectively were found to have positive H pylori infection (P＜0.001). In patients with bleeding peptic ulcers, non-bleeding peptic ulcers and chronic gastritis, polymerase chain reaction for H pylori infection was positive in 54 patients (61%), 70 patients (86%) and 20 patients (54%) respectively (P＜0.001). The sensitivity,positive predictive value and diagnostic accuracy of mucosal polymerase reaction for Hpylori infection were significantly lower in patients with bleeding peptic ulcers (84%, 79%and 81%) than in patients with non-bleeding peptic ulcers (99%, 99% and 98%) (P＜0.001, P＜0.01 and P＜0.001respectively). The sensitivity, negative predictive value and diagnostic accuracy of mucosal polymerase reaction for H pylori were significantly lower in patients with bleeding peptic ulcers (84%, 83% and 81%) than in patients with chronic gastritis (100%, 100% and 100%) (P= 0.02, P= 0.02and P = 0.001).CONCLUSION: Mucosal polymerase chain reaction for detecting H pylori infection is not reliable in patients with bleeding peptic ulcers.