Abstract: Activated lymphocytes derived from cord blood are excellently effective for preventing and treating various types of tumors and various types of infection. With interleukin 2 and/or anti-CD3 antibody, the lymphocytes derived from the cord blood is prepared by segregating lymphocytes from the cord blood and proliferating the segregated lymphocytes directly in vitro or segregating monocytes from cord blood and proliferating the monocytes in vitro. Also, the cord blood-derived activated lymphocytes can be effectively used for preventing recurrence of the diseases and promoting the take of stem cells or other organs.