It has been proposed that a number of chemical-induced cell injuries result from disruption of the ability of the cell to control calcium. Many of the techniques used to develop this theory have relied on indirect measurements of intracellular calcium. The advent of digital imaging fluorescence microscopy has allowed a more direct examination of the relationship between calcium and cell damage. Results indicate that cytosolic calcium does not play a central role in the initiation of oxidative injury in a number of cell types. Changes in calcium homeostasis occur well after the appearance of other indications of cell injury. However, recent studies indicate that a mitochondrial lesion occurs relatively early in the time course of oxidative cell injury. Calcium may play a role in the development of this lesion.