A SU-polysaccharide skin test (SU-PS test) has been employed and studied as a parameter for monitoring the immunological status of OK-432 treated patients who had undergone a curative gastrectomy for a gastric cancer in stages II and III. The median diameter of the erythema (SU-PS value) was found to have no relation to the number of lymphocytes and the serum protein level and was depressed by combined chemotherapy. The SU-PS value was significantly higher in patients not given a splenectomy than in patients who had undergone a patients splenectomy. The spleen is considered the essential organ to focus on in OK-432 immunotherapy.