The effects of the Ca2 + ionophore A2317 on pancreatic amylase and lactate dehydrogenase (LDH) release, cellular electrolyte balance and ultrastructure were studied with the use of incubated pancreatic fragments. A23187 (0.3 micrometer) in the presence of Ca2 +, increased amylase release but at higher concentrations (1-10 micrometer) also increased LDH release and increased uptake of 14C-sucrose with concomitant loss of tissue K + and gain in Na +. The ultrastructure of the majority of acini appeared normal and showed depletion of zymogen granules. Microtubules and microfilaments which have been implicated in the release process were normal or increased in number. In the absence of Ca + the ionophore had no effect on secretion, cellular integrity or ultrastructure. It is concluded that A23187 in the presence of Ca2 + increases amylase release by a mechanism comparable to the terminal steps in stimulus-secretion coupling induced by physiological secretagogues. This provides further evidence that amylase release is mediated by a rise in cell Ca2 + although the mechanisms of the ionophore- and physiological secretagogue-induced rise in Ca + are probably different. High concentrations of ionophore (greater than 1 micrometer) also induce Ca2 + dependent damage in a fraction of the cells.