Results of recent studies from this laboratory have demonstrated that methylprednisolone sodium succinate increases the survival rate of dogs given LD100 Escherichia coli endotoxin. This study was undertaken to determine the effects of methylprednisolone on the baboon infused with live Escherichia coli organisms. Awake baboons were paired by infusing intravenously comparable doses of Escherichia coli during a five hour period. Baboons given methylprednisolone received bolus injections of 30 milligrams per kilogram at 15 minutes after beginning the infusion of Escherichia coli and two hour infusions of 15 milligrams per kilogram at two hour intervals until death or for a 24 hour period. The mortality was unaltered by methylprednisolone. Six of seven baboons that were dying became progressively hypoglycemic, while hypoinsulinemia occurred in all baboons within six hours and was sustained until death. Systemic hypotension was observed. although pressures were variable. Potassium and lactate concentrations increased, while pH remained relatively constant in most baboons. Serum glutamic-pyruvic transaminase and arginase concentrations rose in most baboons dying with 18 hours. Results of morphologic studies revealed the presence of fibrin thrombi in the liver, kidney and adrenal tissue in most baboons. No significant differences in physiologic, metabolic, hematologic or morphologic parameters were observed between treated and untreated baboons.