Sera of rat stimulated by plant lectins PHA (Phytohemagglutinin) and PWM (Pokweed mitogen) were injected to lethal dose irradiated mice 20 hours before irradiation. The survival rates were % 80 in the PWM-induced serum injekted group, % 65 in the PHA-induced serum injekted group respectively. CFUs tests performed before and after radiation showed that the hematopoietic stem cells increased especially in the PWM-induced serum injected group.