The administration of a hemolytic streptococcus preparation, OK-432, is thought to be of therapeutic value in the treatment of cancer patients through a stimulatory effect on the immune system. In order to evaluate any beneficial effect of such an administration, a group of patients with recurrent gastric cancer was studied. This group was randomly subdivided into 3 groups: 1) Intradermal group (ID Group), 42 patients given an intradermal injections of OK-432. 2) Intramuscular group (IM Group), 40 patients given an intramuscular injections of OK-432. 3) Control group (C Group), 39 patients not given injections. Each group was studied in regards to the length of survival, the host immune response and the incidence of side effects. When compared to the IM and C Groups, the ID Group showed improved survival. Accompanying this improved survival, the ID Group also had greater white cell and lymphocyte counts, a greater number of T cells, and a more dramatic skin reaction to the extracted cell wall polysaccharide of hemolytic streptococcus Su-strain (Su-PS). The ID Group, following OK-432 injection, had a 4.8% incidence of fever and a 52.4% incidence of local abscess formation at the injection site. 90% of the IM Group developed fever but abscess formation was absent in all patients. From these results, it was concluded that in the patients tested, intradermal injection of OK-432 appears to be clinically superior to intramuscular injection.