The ontogeny of protein kinase C (PKC) in the hippocampus was studied in 1-week-, 4-week-, and 3-month-old Wistar rats with in vitro receptor autoradiography using [3H]phorbol 12,13-dibutyrate ([3H]PDBu). The developmental pattern of [3H]PDBu binding varied within hippocampal subregions. [3H]PDBu binding in stratum oriens of the CA1 and CA3 sectors and stratum lucidum of the CA3 sector increased to adult levels by 4 weeks. In strata moleculare and granulosum of the dentate gyrus, the binding reached peak values at 4 weeks but declined at 3 months. Interestingly, in stratum lacunosum-moleculare of the CA1 sector, the [3H]PDBu binding activity was the highest at 1 week. There were constant binding activities in stratum radiatum of the CA1 and CA3 sectors and the dentate hilus during the postnatal development. These findings may provide evidence that PKC has a distinct role in different subregions of the hippocampus during postnatal development.