Cellular injury was produced in Ehlrich ascites tumor cells by an inhibitor of the function of the cell membrane [10(-3M) parachloromercuribenzenesulfonic acid (PCMBS)] or by inhibitors of respiration (10(-4M) Antimycin A), glycolysis (10(-4M), iodoacetic acid, IAA), oxidative phosphorylation (10(-3M) 2,4 dinitrophenol, DNP) or by combinations of these in a medium with or without glucose. The contents of Na+, K+, Ca++, Mg++ and intracellular water in the treated cells and controls were correlated with the percentages of ultrastructural changes in the mitochondria of the cells. A moderate negative correlation (r = -0.66) was observed between K+ content of the cells and the condensation of mitochondria in selected experiments where mitochondrial swelling had not yet started. A moderate positive correlation (r = 0.44) was observed between mitochondrial condensation and Na+ content of the cells in the same experiments. K+ and Mg++ content of cells showed a moderate negative correlation (r = -0.58 and -0.65) with mitochondrial swelling in the material of all experiments and Ca++ content a moderate positive one (r = 0.58), but the Na+ content and intracellular water showed no correlation. The percentages of flocculent densities in mitochondria showed a moderate positive correlation (r = 0.43) with the Ca++ content of the cells and a moderate negative correlation (r = -0.61) with the magnesium content of the cells.