This review describes the protein kinases that are involved in long-term potentiation (LTP). The following items are described. 1. Ca2+/calmodulin-dependent protein kinase II (CaMKII) and protein kinase C (PKC) may play pivotal roles in the different phases of the expression of LTP. This involvement has been indicated mainly by using specific inhibitor of these kinases. The involvement of the CaMKII alpha-subunit was confirmed in mutant mice which are deficient in the gene for the subunit. 2. Involvement of persistently active protein kinases in the maintenance of LTP has been proposed and, since then, several studies have focused upon the persistent kinase. Both PKC and CaMKII are possible sources of the persistent kinase activities. 3. Protein kinases other than CaMKII or PKC (ex. protein kinase A, tyrosine kinases, mitogen-activated kinase) also play roles in the expression of LTP. 4. Finally, the importance of postsynaptic density as a device where complex chemical reactions related to neuronal signal transduction occur is discussed.