Calcium balances in ten enterally or parenterally hyperalimented trauma victims were compared as protein intake was manipulated from 50.5 ± 12.8 to 128.0 ± 17.4 gm/day during an isocaloric metabolic balance study. Calciuresis increased as protein intake increased in all subjects, resulting in an average reduction in daily calcium balance of 195 ± 65 mg/day (p< 0.001). There was no difference in fecal calcium in the enterally fed subgroup. Total and “corrected” total serum calcium were lowered, and indirect evidence suggests that ionized calcium was lowered as well. The mechanism of the increase in urinary calcium is not fully elucidated, although it appears to be a direct effect on the kidney rather than an indirect influence of calcium homeostasis. It is suggested that a calorie/nitrogen ratio of about 360 be maintained in enteral and parenteral alimentation of trauma victims. Thus nitrogen balance can be maintained by the increased nonprotein calorie availability, and possible complications of increased calcium mobilization and excretion can be avoided.