A lymphokine in purified form or in the form of a lymphokine containing culture supernatant may be obtained by collecting lymphocytes from an animal or a human sensitized by an immunogen which induces the production of an antibody, selectively concentrating the lymphokine producing cells, forming a fused cell hybrid between the lymphokine producing cells and animal derived tumor cells, cloning the obtained hybrid, selecting the clone which spontaneously produces the lymphokine, culturing the clone to produce the lymphokine, and optionally recovering the lymphokine from the culture and purifying the lymphokine. This process is especially effective for producing interleukin 2, colony stimulating factor, T cells replacing factor, macrophage activating factor or immune interferon.