AbstractCalbindin‐D28K, a cytoplasmic calcium‐binding protein located in restricted regions of mature metanephric kidneys, is expressed in a complex manner by kidneys developing in culture. In developing collecting duct, it is present in all regions and is independent of 1,25‐dihydroxy‐vitamin D3[1,25(OH)2D3]. In developing nephrons, its expression is restricted to the most distal end of the growing tubule, commences during differentiation of specialized tubule segments, and depends completely on the presence of 1,25(OH)2D3. The Wolffian ducts of mesonephric kidneys also express calbindin independently of 1,25(OH)2D3, as do the Wolffian duct‐derived connecting tubules, but mesonephric nephrons show no expression of the molecule. By displaying separate tissue‐specific controls for calbindin expression, cultured kidney rudiments offer a very accessible system for investigation of the control mechanisms involved. © 1994 Wil