The release in vivo and in vitro of stanniocalcin (STC) from the corpuscles of Stannius (CS) of the rainbow trout and the European eel was studied. Intraperitoneal injection of CaCl2 (2.45 mmol.kg-1 fish) leads to an elevation of both ionic and total calcium in the plasma and results in the release of STC from the CS into the blood. Release of STC in vitro is not affected at "physiological" (1.0-1.5 mM) or lower Ca2+ levels in the incubation medium. High levels of Ca2+ (2.5 mM and higher), however, stimulate the release of STC, in particular that of stored STC. We hypothesize that variations in extracellular Ca2+ in the normocalcaemic range do not directly regulate STC release.