Changes in calcium levels during and after resuscitation from severe shock were studied in 22 seriously injured patients who received an average of 21 blood transfusions and 26 mEq supplemental calcium. Total serum proteins (TSP), serum albumin (SA), total calcium (TC), and ionized calcium (CA++), were studied intraoperatively after the tenth transfusion and postoperatively at 5 hours, 15 hours, day 2, day 4, and during convalescene (day 25).The intraopertive TSP fell to 3.7 gm%; the TC and Ca++fell to 7.2 mg% and 1.4 mEq/L. The TSP and SA remained low throughout day 4 (4.8 and 2.6 gm%); the TC was also low on day 4 (7.5 mg%), whereas the Ca++rose to normal (2.1 mEq/L) by day 2. The severity of hypocacemia paralleled the hypoproteinemia, the number of transfusions given during resuscitation, and the duration of shock; paradoxically, hypocalcemia correlated inversely with Ca++supplementation of blood transfusions during resuscitation, suggesting increased extravascular Ca++flux with more severe shock. Further studies in comparably injured patients are needed to identify the concomitant responses of the calcium homeostatic factors such as parathormone in order to help identify the optimal role of calcium manipulation during resuscitation from hypovelemic shock.