The role of dense core secretory vesicles in the control of cytosolic-free Ca 2+ concentrations ([Ca 2+] c) in neuronal and neuroendocrine cells is enigmatic. By constructing a vesicle-associated membrane protein 2–synaptobrevin.aequorin chimera, we show that in clonal pancreatic islet β-cells: (a) increases in [Ca 2+] c cause a prompt increase in intravesicular-free Ca 2+ concentration ([Ca 2+] SV), which is mediated by a P-type Ca 2+-ATPase distinct from the sarco(endo) plasmic reticulum Ca 2+-ATPase, but which may be related to the PMR1/ATP2C1 family of Ca 2+ pumps; (b) steady state Ca 2+ concentrations are 3–5-fold lower in secretory vesicles than in the endoplasmic reticulum (ER) or Golgi apparatus, suggesting the existence of tightly bound and more rapidly exchanging pools of Ca 2+; (c) inositol (1,4,5) trisphosphate has no impact on [Ca 2+] SV in intact or permeabilized cells; and (d) ryanodine receptor (RyR) activation with caffeine or 4-chloro-3-ethylphenol in intact cells, or cyclic ADPribose in permeabilized cells, causes a dramatic fall in [Ca 2+] SV. Thus, secretory vesicles represent a dynamic Ca 2+ store in neuroendocrine cells, whose characteristics are in part distinct from the ER/Golgi apparatus. The presence of RyRs on secretory vesicles suggests that local Ca 2+-induced Ca 2+ release from vesicles docked at the plasma membrane could participate in triggering exocytosis.