AIM: Prior Helicobacter pylori (H pylori) infection has often been underestimated. These underestimations have misled physicians attempting to determine the significance between H pylori and certain gastrointestinal lesions such as intestinal metaplasia, atrophic gastritis, and gastric cancer. Our study endeavored to detect past H pylori infections accurately, easily,and rapidly with the newly developed immunoblot kit, Helico Blot 2.1.METHODS: Thirty-three patients, including 25 H pylori infected and 8 uninfected cases, were enrolled in our study. All patients received consecutive gastroendoscopic examinations and 13C-urea breath test (UBT) tests at 6-or 12-mo intervals for up to 4 years. Serum samples were obtained from each patient at the same time. Intragastric H pylori infection was confirmed in accordance with the gold standard. Twenty-five H pylori-infected patients received triple therapies after initial bacterial confirmation,and were successful in eradicating their infections. Serially obtained sera were tested by means of Helico Blot 2.1.RESULTS: Current infection marker detected by Helico Blot 2.1 was unreliable for representing ongoing H pylori infection. Only 35 and 37 ku antibodies of H pylori had significant seroconversion rates 1 year after having been cured. The seropositive rates of 116 ku (cytotoxin-associated antigen [CagA]) and Helico Blot 2.1 were nearly 100%during 4-year follow-up period. Both CagA antigen and Helico blot 2.1 could serve as indicators of long-term H pylori infection.CONCLUSION: Helico Blot 2.1 can detect past H pylori infections for up to 4 years, and is the best method to date for detecting previous long-term H pylori infection.