The expression of four genes: zif/268, c-fos, tubulin and alpha Ca2+/calmodulin-dependent protein kinase II (alpha CAMKII) was studied following the induction of LTP in Schaffer collateral CA1 neurone synapses in rat hippocampal slices maintained in vitro. Levels of c-fos mRNA and tubulin (T26) mRNA in area CA1 were unchanged after induction of LTP, however, zif/268 and alpha CAMKII mRNA levels showed a significant increase compared to non-potentiated controls. It is possible, therefore, to measure changes in gene expression using in situ hybridisation following induction of LTP in vitro and these results strengthen the theory that zif/268 and alpha CAMKII are involved in some aspect of the induction or maintenance of hippocampal LTP.