Cell-free lysates of human peripheral blood lymphocytes contained two casein kinase activities and two histone kinase activities, which could be separated by chromatography on DEAE-Sephadex. 2. Neither of the casein kinase activities were stimulated by cyclic AMP. The major activity was eluted from DEAE-Sephadex between 0.4 and 0.45M-KCl, had a molecular weight of approx. 130,000 (sucrose density gradients) and was stimulated by KCl (maximum 150mM). It also formed higher-molecular-weight aggregates when centrifuged in sucrose gradients containing 150mM-KCl. The minor activity was not retained by DEAE-Sephadex, had a molecular weight of approx. 50,000 and was not stimulated by KCl. 3. The major histone kinase activity was stimulated by cyclic AMP and was eluted from the DEAE-Sephadex column between 0.05 and 0.2M-KCl. The other activity was not stimulated by cyclic AMP and was insensitive to the rabbit muscle protein kinase inhibitor. 4. Evidence was obtained suggesting that the lymphocyte casein kinases were located primarily in the nuclei.
