Abstract. Stanniocalcin-immunoreactive cells were local ized in the corpuscles of Stannius of a holostean fish, the garpike (Lepisosteus osseus), using antisera against salmon and trout stanniocalcins and the peroxidase-antiperoxidase and protein A-gold immunohistochemical methods. The stanniocalcin-immunoreactive cells were periodic acid-Schiff-positive, and antibody staining was abolished if the antiserum was preabsorbed with corpus cle homogenate. Immunocytochemistry revealed two re active cell types in the glandular parenchyma, and im munoreactivity was confined to the secretory granules. Staining of the granules was also abolished when the antisera were blocked with crude corpuscle homogenate. When corpuscle extracts from garpike were subjected to sodium dodecyl sulphate-polyacrylamide gel elec trophoresis and Western blot analysis, a single dense band was evident with a molecular weight of ^68 kDa under non-reducing conditions, whereas three bands were observed (^29, -31, and ^3 4 kDa) under reduc ing conditions. Staining of all bands disappeared follow ing preabsorption of the antiserum with salmon stanniocalcin, trout stanniocalcin, or garpike corpuscle extract. The results are compared with stanniocalcins from an other extant holostean, the bowfin (Amia calva), and from more modern bony fishes, the teleosts.