Abstract: A biologically active lymphokine fraction which exhibits macrophage activation activity and lymphotoxin activity is prepared from large scale supernatant culture fluids of human lymphoblastoid cultured cell lines grown in the presence of human serum to minimize antigenicity. Growth of lymphoblastoid cells from human lymphoblastoid cultured cell lines is effected and the supernatant culture fluids are harvested, concentrated and clarified. The supernatant culture fluids are then extracted with trichloroacetic acid, guanidine hydrochloride, sodium dodecyl sulfate or perchloric acid as the extracting solvent followed by removal of the solvent. Further purification of the lymphokine fraction can be achieved by treatment with guanidine hydrochloride or sodium dodecyl sulfate as a dissociating solvent and by subjecting the lymphokine fraction to gel filtration, sodium dodecyl sulfate gel electrophoresis and/or high pressure liquid chromatography.