AIM: Prior Helicobacter pylori (H pylori) infection has often been underestimated. These underestimations have misled physicians attempting to determine the significance between Hpyloriand certain gastrointestinal lesions such as intestinal metaplasia, atrophic gastritis, and gastric cancer. Our study endeavored to detect past Hpyloriinfections accurately, easily, and rapidly with the newly developed immunoblot kit, Helico Blot 2.1. METHODS: Thirty-three patients, including 25 Hpylori infected and 8 uninfected cases, were enrolled in our study. All patients received consecutive gastroendoscopic examinations and ~(13)C-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 py/orihad 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. AIM: Prior Helicobacter pylori (H pylori) infection has often been underestimated. These underestimations have misled physicians attempting to determine the significance between Hpyloriand certain gastrointestinal lesions such as intestinal metaplasia, atrophic gastritis, and gastric cancer. Our study endeavored to detect past Hpylori infections accurately , easily, and rapidly with the newly developed immunoblot kit, Helico Blot 2.1. METHODS: Thirty-three patients, including 25 Hpylori infected and 8 uninfected cases, were enrolled in our study. All patients received consecutive gastro-endological examinations and ~ (13) C -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 Results: Current infection marker detected by Helico Blot 2.1 was unreliable for current H pylori infection. Only 35 and 37 ku antibodies of H py / orihad significant seroconversion rates 1 year after having Both CagA antigen and Helico blot 2.1 could serve as indicators of long-term (cytotoxin-associated antigen [CagA]) and Helico Blot 2.1 were nearly 100% during 4-year follow- 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 long term H pylori infection.