The basal expression of the protein products of the inducible immediate early genes (IEGs), Fos, Jun, and Krox 24, was investigated in rat hippocampus using immunocytochemical visualization methods with antisera specific for Fos only, Fos and the Fos-related antigens (FRAs), the Jun family, and Krox 24 (previously described as TIS 8, egr-1, NGF-IA or zif 268). In the normal adult rat brain basal levels of Jun, Krox 24 and Fos-related antigens but not Fos were seen within the hippocampus. More specifically very high basal levels of Jun were seen in the dentate granule cells with high basal Krox 24 levels seen in the CA1-subiculum region of the rat hippocampus. Basal FRAs but not Fos-positive cells were seen at low levels in the dentate granule cells. The implications of these results to the functioning of IEG proteins in hippocampal neurons is discussed.