The protein nucleobindin 1 (NUCB1; also known as CALNUC or Nuc) contains an intriguing combination of DNA- and calcium-binding motifs, a trait that it shares with the protein nucleobindin 2 (NUCB2; also known as nesfatin). NUCB2 has been implicated in several aspects of metabolic control and has been identified in a number of endocrine organs. No such comprehensive mapping of NUCB1 has been presented. We have explored the expression and distribution of NUCB1 in tissues and cells of the mouse endocrine system, with particular focus on the endocrine pancreas. Using reverse transcription plus the polymerase chain reaction (RT-PCR) and Western blot, we demonstrate that NUCB1 is present in the endocrine islets of Langerhans but absent from the exocrine acinar cells. Immunofluorescence studies have revealed that all islet cell types contain NUCB1, including the NUCB2-expressing beta cells. RT-PCR, Western blot and immunofluorescence have shown that NUCB1 is expressed in the pituitary, thyroid, parathyroid, gastrointestinal tract, adrenals and gonads. However, within these tissues, NUCB1 expression is not ubiquitous. For example, in the testis, NUCB1 occurs in the seminiferous tubules but not in the Leydig-cell-containing interstitial tissue. Similarly, the lamina propria of the duodenum lacks NUCB1, despite its presence in enterocytes. Where present, NUCB1 consistently appears to be associated with the Golgi apparatus. Thus, NUCB1 is broadly, but not ubiquitously, expressed in cells of the mouse endocrine system. Together with its location in the Golgi apparatus and its putative Ca(2+)-binding ability, this distribution suggests a role for NUCB1 in Ca(2+) handling/sensing in secretory cells.