Clinical usefulness of cytokines in cancer treatment has been described. Cytokines presently used in clinical practice are IFNs, IL-2, and hematopoietic growth factors. IFNs and IL-2 used with an expectation of direct antitumor effect of these cytokines have been proven to be specifically effective against certain types of tumors. Hematopoietic growth factors have been used as the adjuvant drugs in cancer treatment and proven to be effective against neutropenia and associated infections after chemotherapy and bone marrow transplantation. Future development of new cytokines and trials on the combination among cytokines and cytokines with chemotherapeutic agents, will promote the usefulness of cytokines in cancer treatment.