Sulfate was infused intravenously into dogs as the salt of sodium, potassium, or the organic amine, "tris." Calcium clearance was more closely correlated with sodium clearance than with sulfate excretion. When sodium excretion was low, little calciuresis occurred. The clearance of free calcium ions was calculated, making allowance for the electrostatic association between calcium and sulfate ions in the urine. The relationship between free calcium ion clearance and sodium clearance closely resembled that previously observed during saline or mannitol diuresis. Thus, in the absence of hypercalcemia, calcium excretion in the dog, in these experiments, is dependent primarily on the simultaneous sodium excretion, which determines free calcium ion excretion, and secondarily on the concentration of complexing anions in the urine, which determines how much additional calcium is excreted in bound form.