We isolated rat presenilin-1 (PS-1; also called S182 previously) cDNA from total brain RNA by using a reverse transcription-polymerase chain reaction (RT-PCR) technique with primers homologous to the conserved sequences of human and mouse PS-1. Rat PS-1 cDNA encoded 468 amino acids (aa) and the deduced aa sequence was highly homologous to those of the human (88.4%) and mouse (92.7%). Northern blot analysis of the rat PS-1 cDNA revealed two mRNA species in rat neurotypic pheochromocytoma and glioma cell lines (PC-12 and C6, respectively) that migrated at rates corresponding to approximately 3.0 and 7.5 kb.