Calcium-activated neutral proteinase (calpain) is a ubiquitous, cytosolic endopeptidase which is believed to play a role in many neural functions. In the present study, we examined the transcriptional and translational expression of microcalpain (calpain) and millicalpain (mcalpain) isoforms and the endogenous inhibitor calpastatin in rat and bovine spinal cord, brain stem, cerebellum, and cerebral cortex tissues using reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blotting. In rat central nervous system (CNS) samples, the calpain and mcalpain transcriptional expression was highest in white matterenriched areas. Calpastatin mRNA expression demonstrated no significant differences among the CNS areas. Calpain and calpastatin translational expression levels were greatest in the spinal cord. In bovine CNS, calpain transcriptional expression was greatest in the spinal cord, while other CNS regions showed no significant differences. Bovine mcalpain transcriptional expression was similar among various CNS regions but marginally greater in the cortex. Translational expression of bovine calpain was greatest in the brain stem, while that of calpastatin was highest in the cerebral cortex. These results indicate that calpain expression varies among different CNS regions and is often highest in white matter-enriched areas.