The molecular identity of a gene which encodes the pore-forming subunit (α1G) of a member of the family of low-voltage-activated, T-type, voltage-dependent calcium channels has been described recently. Although northern mRNA analyses have shown α1G to be expressed predominantly in the brain, the detailed cellular distribution of this protein in the central nervous system (CNS) has not yet been reported. The current study describes the preparation of a subunit specific α1G riboprobe and antiserum which have been used in parallel in situ mRNA hybridization and immunohistochemical studies to localize α1G in the mature rat brain. Both α1G mRNA and protein were widely distributed throughout the brain, but variations were observed in the relative level of expression in discrete nuclei. Immunoreactivity for α1G was typically localized in both the soma and dendrites of many neurons. Whilst α1G protein and mRNA expression were often observed in cells known to exhibit T-type current activity, some was also noted in regions, e.g. cerebellar granule cells, in which T-type activity has not been described. These observations may reflect differences between the subcellular distribution of channels that can be identified by immunohistochemical methods compared with electrophysiological techniques.