As the introduction to a special issue of Oncology on the role of cytokines for cancer treatment, this article summarizes their various current uses. Interferons, interleukin-2 and hematopoietic factors are extensively used for the treatment of hematopoietic as well as nonhematopoietic malignancies, either as the main therapeutic agents or as an adjuvant. Combined usage of several cytokines, or cytokines and chemotherapeutic agents has been tried. Research on gene therapy using cytokines is in progress and expected to become a future modality of cytokine usage in cancer treatment.