Lymphokines are defined as nonimmunoglobulin secretory products of activated lymphocytes with a wide range of potent physiological effects on inflammation and immune responses. In this review, we summarized the recent development in lymphokine researches, including biochemical and immunological approaches. An increasing number of assay methods enabled us to detect various lymphokine activities released in the culture medium of lectin activated lymphoid cells. However, some of the results in a number of independent studies about lymphokines were rather complicated for precise interpretation, since the lymphoid cell-culture medium comprises a mixture of very heterogeneous lymphokines molecules. This problem has now been overcome by generating hybridomas producing rather homogeneous lymphokine. By utilizing such relatively homogeneous lymphokines, we analyzed the mechanism of cytoxic T lymphocyte (CTL) generation, and discussed a possibility for utilization of this approach to the future antitumor immunotherapy.