Proliferating cell nuclear antigen (PCNA) plays a pleiotropic role in DNA replication, excision repair of injured DNA and apoptosis. We found that PCNA protein is expressed predominantly in CA3 pyramidal neurones in hippocampal slices cultured from 1-week-old rats. Immunoblotting analysis revealed that this PCNA expression is enhanced by u.v. irradiation with no effect on neuronal viability. These results suggest that expression of PCNA in non-proliferating central neurones is associated with repair of injured DNA.