Cytosolic calcium oscillations may permit cells to respond to information provided by increases in [Ca²⁺]_i while avoiding prolonged exposure to constantly elevated intracellular Ca²⁺ concentrations. In this study, we demonstrated that agonists could induce Ca²⁺ oscillations in human bladder epithelial cells. Application of 10 µM acetylcholine or 200 nM bradykinin triggered an initial Ca²⁺ transient that was followed by periodic [Ca²⁺]_i oscillations. The oscillations did not depend on extracellular Ca²⁺. 8-Br-cGMP abolished acetylcholine- or bradykinin-induced oscillations. Elevation of cellular cGMP by dipyridamole, an inhibitor of cGMP-specific phosphodiesterase, also terminated the [Ca²⁺]_i oscillations. The inhibitory effect of cGMP could be reversed by KT5823, a highly specific inhibitor of protein kinase G, suggesting that the action of cGMP was mediated by protein kinase G. Comparison of the effect of cGMP with that of Xestospongin C (XeC), an inhibitor of IP₃ receptor, revealed similarities between the action of cGMP and XeC. Therefore, it is likely that cGMP and PKG may target on signal transduction step(s) leading to the IP₃ receptor-mediated Ca²⁺ release.