Unipolar brush cells (UBCs) are excitatory neurons in the mammalian cerebellum and cochlear nuclei (CN), including the CN of primates, as shown only recently. UBCs are readily identified by their expression of the calcium-binding protein calretinin (CR), except for those of the primate CN that hardly immunostain for CR. The present findings corroborate the existence of UBCs in the CN of a primate,Callithrix. Furthermore, evidence is presented for UBCs in the cerebellum and a small subpopulation of UBCs in the CN ofCallithrixto express the calcium-binding protein calbindin (CB). This may be unique forCallithrixas CB-expressing UBCs have not been recognized in any other mammal. Presence of CB but not CR in UBCs of theCallithrixCN may indicate a certain interchangeability between these two calcium-binding proteins.