A chelator, dichloromethane diphosphonate (Cl2MDP), used to treat for malignancy-induced hypercalcemia, has nephrotoxic potential. An acute animal model developed to examine the mechanism was used to further characterize the renal effects. NAG enzymuria appears to be an early premonitor of injury. Ultrastructurally, an increase in size and number of protein-containing phagolysosomal reabsorption droplets in proximal convoluted tubules associated with proteinuria precedes advent of tubular cell necrosis indicating these organelles to be a potential target site for Cl2MDP in the kidney. In vitro studies using rabbit cortical tubules and rat brush border membrane vesicle preparations suggest that the renal toxicity is not due to perturbation of phosphate transport or oxidative metabolism. An operational hypothesis emerges indicating that Cl2MDP may be protein bound affecting carrier protein charge facilitating glomerular leakage with tubular accumulation via protein transport. Cl2MDP may induce critical cation perturbation at the subcellular level as the mechanism of cell death.