The peritoneum is one of the most frequent sites of recurrent gastric carcinoma after curative treatment, despite the administration of pre- and/or postoperative systemic chemotherapy. Indeed, the prognosis of peritoneal carcinomatosis from gastric carcinoma continues to be poor, with a median survival of less than one year with systemic chemotherapy. Whereas the prognosis of peritoneal carcinomatosis from colorectal cancer has changed with the development of locally administered hyperthermic intraperitoneal chemotherapy (HIPEC), survival results following carcinomatosis from gastric cancer remain disappointing, yielding a 5-year survival rate of less than 20%. Innovative surgical therapies such as intraperitoneal immunotherapy therefore need to be developed for the immediate postoperative period after complete cytoreductive surgery. In a recent randomised study, a clinical effect was obtained after intraperitoneal infusion of catumaxomab in patients with malignant ascites, notably from gastric carcinoma. Catumaxomab, a nonhumanized chimeric antibody, is characterized by its unique ability to bind to three different types of cells: tumour cells expressing the epithelial cell adhesion molecule (EpCAM), T lymphocytes (CD3) and also accessory cells (Fcγ receptor). Because the peritoneum is an immunocompetent organ and up to 90% of gastric carcinomas express EpCAM, intraperitoneal infusion of catumaxomab after complete resection of all macroscopic disease (as defined in the treatment of carcinomatosis from colorectal cancer) could therefore efficiently treat microscopic residual disease.