Abstract Using a monoclonal antibody the translocation of the Ca 2+-dependent protein kinase C (PKC) isoenzymes α/β was studied in hippocampal slices after stimulation of glutamate receptors or induction of long-term potentiation. In submerged slices preincubated for 60 min in a medium usually used in electrophysiological studies, cytosolic PKC was not detectable and the amount of membrane-associated enzyme was increased. The treatment of these slices with 10 −6 M phorbol-12,13-dibutyrate induced a time-dependent translocation of α/β PKC from the membrane-associated into the membrane-inserted state. The glutamatergic agonists N-methyl- d-aspartate, quisqualate and trans-ACPD did not cause a membrane insertion of α/β PKC as observed for the phorbol ester when applied alone or in combination. Furthermore, 2 min and 15 min after induction of LTP in the Schaffer collateral-CA1 pathway the distribution of α/β PKC between the two membrane fractions remained unchanged. An increase in the total amount of PKC immunoreactivity was measured immediately after tetanization (142.6% of controls). The data suggest that a membrane insertion of α/β PKC is not a prerequisite for the LTP-induced increased phosphorylation of PKC substrates and that the enzyme might be recruited from a previously inactive pool.