The study group consisted of 35 patients with early gastric cancer, 16 of whom were admitted for preoperative immunotherapy. Ten to 40 K.E. of OK-432 was injected intralesionally by endoscope, and then gastrectomy was performed. After the intralesional injection, fever, nausea, vomiting and epigastralgia occurred. In cancer lesion and regional lymph node, histological findings from OK-432 treated group were compared to those of the control group. Lymphoid cell infiltration at cancer lesion was marked in OK-432 treated group, and degenerated cancer cells were found in 3 cases. On the other hand, lymphoid follicles showed a marked statistical increase in OK-432 treated group. Also the cases with marked lymphoid follicle showed increased numbers of peripheral blood lymphocyte. From the results, intralesional injection of OK-432 may confirm the tumor-associated antigenicity and serves as a useful method to potentiate the specific and/or non-specific immunity in regional lymph nodes.