The effects of inorganic phosphate-induced hypocalcaemia on experimental digitalis intoxication were studied in 75 dogs. In the control digitalized group four animals died of ventricular fibrillation, eight remained with frank signs of intoxication at the end of the 180 min period, and in three animals the ECG returned to normal. Intravenous infusion of inorganic disodium monopotassium phosphate induced a return to normal of the ECG, in all cases, in 38·5 ± 22 min. Infusions of a buffered glucose or a potassium chloride solution were ineffective. In the phosphate treated group, a marked decrease in serum calcium was observed; in the other groups changes in serum Ca were not significant. Potassium, pH, and HCO3− changes were not significant in any group.