Ionized calcium (Ca2+) and ionized magnesium (Mg2+) are important intracellular “second messengers‘’ and control excitation-contraction coupling, excitation-secretion, oxidative phosphorylation, and mitochondrial acid-base balance. The present study examines the effect of septic shock on serum (Ca2+) and (Mg2+). Five adult female baboons were subjected to liveE. coliseptic shock and then resuscitated. Three baboons served as controls. Ca2+was measured by the Orion SS-20 flow-through calcium electrode and Mg2+calculated by the method of Killen. Other measurements included: total calcium, bound calcium, total magnesium, bound magnesium, phosphate, albumin, globulin, hemotocrit, and total protein.This study shows that there are significant disturbances of Ca2+and Mg2+during septic shock in the baboon. These disturbances may in part explain cellular dysfunction during shock including: decreased myocardial contractility, inappropriate secretion of endocrine cells, decrease in oxidative phosphorylation, and mitochondrial acidosis.