Previous immunocytochemical studies have shown that protein kinase CK2 is mostly detected both in the cytoplasm and the nucleus of most cells. In the present study, CK2 was detected in highly purified plasma membrane preparations from rat liver. The protein kinase could be released from the membranes by high salt extraction (>1 M NaCl). Plasma membranes prepared from SF9 insect cells expressing the alpha- and beta-subunits of CK2 also contained a significant amount of oligomeric CK2. Furthermore, it was demonstrated in this cell system as well as in rat liver plasma membranes, that the beta-subunit of the kinase is the targeting subunit which mediates the tight association of the enzyme to plasma membrane components. Binding studies using membranes and recombinant proteins corresponding to different regions of the beta-subunit suggest that a functional domain previously shown to be involved in the binding of polyamines may also participate to the binding of CK2 to membranes. Modification of membranes by trypsin and phospholipases indicated that the binding process may require both membrane protein(s) and phospholipids. Interestingly, it was observed that the amount of membrane-bound CK2 in liver of embryos and new born rats increases dramatically after birth and persists during the postnatal stages of development.