The importance of calcium regulation in toxic cell injury. Studies utilizing the technology of digital imaging fluorescence microscopy. The regulation of ions within the cell is of critical importance in both acute and chronic toxicology. Recently, new methods have been developed for measuring such changes in living cells and correlating them with studies of structure, function, and biochemistry. A major revolution has occurred from the linkage between the computer and the light microscope, which has resulted in the use of digital imaging fluorescence microscopy and video intensification microscopy coupled with image analysis. These methods have already yielded much additional information and it is anticipated that their further application by pathologists and toxicologists will continue to uncover the important role of ion deregulation and toxic cell injury. 