Complete regression of high-grade lymphoma is extremely rare. We report 1 such case that might have been conceivably mediated by Ganoderma lucidum (Lingzhi), an immunomodulatory herbal medicine. A 47-year-old man presented with epigastric pain. Endoscopy revealed a large gastric ulcer, which on biopsy was diagnostic of large B-cell lymphoma. At gastrectomy 11 days later, no evidence was found of large B-cell lymphoma despite thorough sampling. Instead, there was a dense and permeative infiltrate of CD3(+) CD8(+) cytotoxic small T lymphocytes spanning the whole thickness of the gastric wall. In situ reverse transcription polymerase chain reaction for T-cell receptor beta-chain family did not detect a monoclonal T-cell population. We postulate that the cytotoxic T cells may represent an active host-immune response against the large B-cell lymphoma that resulted in a complete regression. On questioning, the patient had taken megadoses of Ganoderma lucidum, which might have triggered the successful immune reaction.