We describe the actions of 2,3-butanedione monoxime (BDM) on calcium responses in secretory cells. Our studies were prompted by the widespread use of BDM as a myosin-ATPase inhibitor. Application of 10 mM BDM almost completely inhibited agonist-evoked amylase secretion from mouse pancreatic acinar cells. This action might be interpreted as indicating a role for myosin in secretion. However, BDM alone elicited a calcium response in single cells and this calcium signal was sufficient to activate calcium-dependent chloride currents. Furthermore, in some cases, BDM potentiated agonist-evoked calcium signals but almost always blocked agonist-evoked calcium oscillations. These effects of BDM were not due to an action on calcium influx pathways but rather to direct effects on IP(3)-sensitive stores. We conclude that BDM cannot be used for unequivocal identification of the involvement of myosin motors in a cellular response. Further, our evidence suggests that BDM can act directly to modify the opening of IP(3) receptors.