Quantal catecholamine secretion evoked from individual pheochromocytoma (PC12) cells by exposure to mitochondrial inhibitors and uncouplers was monitored in real time using amperometry. Cyanide (0.05-5 mM) caused a concentration-dependent increase in the frequency of amperometric events. This secretory response was abolished by removal of extracellular Ca2+ and by the application of Cd2+ (200 mu M), a nonselective blocker of voltage-gated Ca2+ channels. Secretion was also inhibited by ca. 75% following pretreatment of cells with omega-conotoxin GVIA to inhibit N-type Ca2+ channels selectively. Secretion was also detected when cells were exposed to rotenone (10 mu M), dinitrophenol (250 mu M) and p-trifluoromethoxyphenyl hydrazone (1 mu M) and, as for cyanide, these secretory responses were abolished by removal of extracellular Ca2+ or application of 200 mu M Cd2+. These results indicate that, like hypoxia, mitochondrial inhibitors and uncouplers evoke catecholamine secretion from PC12 cells which is wholly dependent on Ca2+ influx through voltage-gated Ca2+ channels.