Regression of high-grade gastric B-cell lymphoma after eradication of Helicobacter pylori with antibiotic therapy has recently been shown in a very small number of patients. We describe here a patient with a 5-cm polypoid gastric lymphoma, who received a 7-day course of triple therapy when the histopathology was unknown. A second endoscopic examination 4 weeks later showed partial tumor regression without biopsy evidence of malignancy. Endoscopic mucosectomy was performed 8 weeks after the initial diagnosis. Again, in the histological analysis of the specimen, no evidence of B-cell lymphoma could be found. To confirm that the original biopsies were from the same patient, DNA analyses were carried out which gave identical results. This case suggests that a subgroup of primary gastric B-cell lymphomas responds to eradication of H. pylori with antibiotic therapy.