The efficacy of Levamisole (LMS) was studied on prolongation of patient survival and modulation of cellular immunity in a total of 220 cases of gastric cancer (136 cases for control and 84 cases for LMS group). In the study, detailed analyses were performed in 64 cases of stage Ⅲ, in which LMS therapy was effective and influence of background factors was minimum (32 cases for control and 32 cases for LMS group). LMS was administered 150mg/day for three consecutive days every other week beginning from three days before operation, and was continued more than than two months and upto two years. The results obtained were as follows: 1) In cases of gastric cancer, the survival rate of the LMS group, was significantly higher than that of the control group (p<0.05). Furthermore, the efficacy of LMS on prolongation of survival rate was remarkable in the group of stage Ⅲ (p<0.05). 2) A detailed study in the group of stage Ⅲ was performed and resulted in the following: First, when stage Ⅲ cases were classified into curative and noncurative cases, LMS was effective in prolonging the survival of patients who received curative resection. Secondly, the efficacy of LMS was investigated in terms of tumor size. No difference in patient survival was observed between the control and LMS group, when tumor size was less than 3.9cm or more than 8.0cm in diameter. However, a significant effect of LMS therapy was detected for cases whose tumor was between 4.0cm and 7.9cm in diameter and depth of invasion was se (P<0.05). Thirdly, influence of lymph node metastasis on the effect of LMS was analysed. LMS was effective to a significant degree if the metastasis did not extend beyond lymph nodes classified in group I (n(1)) (p<0.05). Fourthly, when localization or histopathological grading of tumor was considered, the survival rate of LMS group tended to be high if the tumor was localized in the bulk of the corpus and belonged to a undifferentiated type. Fifthly, the (v) factor, grade of invasion into veins, was evaluated. LMS was effective in cases of v(0). And also, the efficacy of LMS was observed in cases classified as INF β in terms of form of infiltration. 3) Mitogen responses, cell number and T-cell percentage of peripheral blood lymphocytes and also PPD skin test were examined to evaluate immunological status of gastric cancer patients receiving LMS therapy. The data suggested that LMS activated promptly and normalized the cellular immunity in cases of advanced gastric cancer classified into stage Ⅲ and Ⅳ in which cellular immunity was reduced. By contrast, it was ineffective for cases of gastric cancer at early stages classified into stage Ⅰ and Ⅱ.