Suspensions of cells from Hodgkin disease tumors were separated by velocity sedimentation in an isokinetic Ficall gradient. The separated cells were cultured with mitogens. The modal population of lymphocytes from the tumor contained 50%-75% of all lymphocytes separated from the tumor of each studied patient. Despite the fact that these cells appeared to be mature lymphocytes, the majority of which formed nonimmune E rosettes with sheep red blood cells, they showed a lack of responsiveness to phytohemogglutinin which was almost complete in all but one patient. Lymphocytes which had been obtained in suspension and purified by identical methods from tonsils and spleens without tumors did respond to stimulation by phytohemagglutinin.