We investigated, by in situ hybridization histochemistry, the cellular localization of the mRNA encoding a vitamin D-dependent calcium-binding protein (calbindin D28) in rat brain and peripheral organs. Using a [35S]cRNA probe under high stringency conditions, specific mRNA was found in tissues well known for their calbindin D28 content, e.g. renal distal tubules, cerebellar Purkinje cells and dentate gyrus granule cells. Tissue devoid of this protein, such as liver, also lacked specific mRNA. In situ hybridization histochemistry allows the precise identification of cells expressing calbindin D28 and offers a new approach to study its regulation and possible role, e.g. in neuronal function.