Fluctuation of the postoperative lymphocyte blastformation rates against phytohemagglutinin (abbreviated as the blastoformation rate) were examined in gastrointestinal cancer patients administered with levamisole 150 mg/day, three consecutive days, every other week from the third day before operation comparing with the values of the control cases. In the cases of curative resection the postoperative blastformation rate of the control group decreased due to operation damage from the first to the third postoperative week and recovered at the fourth week. But, the postoperative blastformation rates of the levamisole group did not decrease, moreover, increased continuously to the fourth week. This result would induce the development of survival ratio in the gastrointestinal cancer patients with administered levamisole.