Calcium-binding protein (CaBP) was localized with peroxidase-labeled antibody in human jejunum and kidney, and in kidney and pacreas of several animal species. The protein was associated with plasma membrane and intercellular space of jejunal absorptive cells. It was present in a specific population of renal tubule cells and in pancreatic islet cells. Immunohistochemical staining of intestinal CaBP with antibody to renal CaBP indicates structural similarity between the two proteins despite their different molecular weight.