In eleven patients with gastric cancer who could not be operated on because of advanced age, refusal of surgery, or the presence of complications, the streptococcal preparation OK-432 was administered, both intradermally and by direct injection into the tumor under endoscopic guidance. Via gastric x-ray and endoscopic examinations, the tumor was observed to disappear in two cases-one advanced cancer and one early gastric cancer endoscopically. Particularly in the latter case repeated biopsies revealed no evidence of cancer cells. All patients developed fever after intratumor injection, but in no case was it necessary to discontinue administration, and no other serious side effects were noted. The endoscopic injection of OK-432 appears to be a safe and useful form of therapy for gastric cancer unsuitable for surgery.