The protective implications of transfusion hepatitis with respect to cancer are examined. It was observed that three patients suffering from advanced stomach cancer (IIIrd and IVth stage TNM), submitted to palliative surgery, contracted a probably transfusional hepatitis in the postoperative period and thereafter showed remission of the basic disease. Mechanisms of aspecific immunitary activation and/or a direct cytotoxic action on the part of the virus are postulated.