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AIM: To detect and evaluate the antibodies against Helicobacter pylori ( H pylori) neutrophil-activating protein (HP-NAP) in patients with gastric cancer and other gastroduodenal diseases.METHODS: Recombinant HP-NAP was prepared from a prokaryotic expression system in Escherichia coli. Serum positivity and level of HP-NAP-specific antibodies in sera from 43 patients with gastric cancer, 28 with chronic gastritis, 28 with peptic ulcer, and 89 healthy controls were measured by rHP-NAP-based ELISA. rHP-NAP-stimulated production of interleukin-8 (IL-8) and growth-related oncogene (GROα) cytokines in the culture supatant of SGC7901 gastric epithelial cells was also detected. RESULTS: The serum positivity and mean absorbance value of HP-NAP-specific antibodies in the gastric cancer group (97.7% and 1.01 ± 0.24) were significantly higher than those in the chronic gastritis group (85.7% and 0.89 ± 0.14, P < 0.005) and healthy control group (27.7% and 0.65 ± 0.18, P < 0.001). The sensitivity and specificity of ELISA for the detection of HP-NAP-specific antibodies were 95.5% and 91.5%, respectively. HP-NAP could slightly upregulate IL-8 production in gastric epithelial cell lines but had no effect on GROα production. CONCLUSION: Infection with virulent H pylori strains secreting HP-NAP is associated with severe gastroduodenal diseases, and HP-NAP may play a role in the development of gastric carcinoma. rHP-NAPbased ELISA can be used as a new method to detect H pylori infection. The direct effect of HP-NAP on gastric epithelial cells may be limited, but HP-NAP may contribute to inflammatory response or carcinogenesis by activating neutrophils.