Reduction of the temperature from 37 C to 18, IS, 10 or 0 C evoked a graded release of vasopressin from bovine neurohypophyses incubated in vitro in Locke's solution. Cold temperature was still effective in releasing vasopressin when Na was replaced by Li, K, Cs or Tris in the incubation medium but was inhibited by high concentrations of Ca, Mg or La. Low temperature caused the simultaneous release of vasopressin, ATP and protein from neurohypophyses in stoichiometric amounts comparable to their relative proportions in neurosecretory granules. At the same time, the release of cytoplasmic markers, LDH and K, was decreased. These results suggest that cold-induced release of vasopressin occurs by the process of exocytosis and not by generalized cell damage. In parallel with studies on coldinduced muscle contraction, cold-induced vasopressin release is more prominent in Ca free solution, is inhibited by replacement of NaCl with sucrose, and is potentiated by caffeine.These results suggest that mobilization of intracellular calcium may be involved in cold-induced release of vasopressin. The study also indicated that caution should be exercised by those who study the physiology or morphology of neurohypophyses which are exposed to low temperature. (Endocrinology94: 234, 1974