Corticosteroids have been reported to potentiate infections, and yet recent clinical and experimental studies have documented their therapeutic effectiveness in both septic and endotoxin shock. This study was designed to determine if methylprednisolone sodium succinate (MP) affects the clearance of live E coli organisms from peripheral blood of dogs. The experimental group was pretreated with 30 mg/kg of MP, and controls received equal volumes of saline. Both control and MP-pretreated dogs significantly reduced the number of E coli in peripheral blood by almost two orders of magnitude; however, there was no significant difference in clearance of E coli organisms between the two groups. An initial leukopenia occurred in both groups after E coli injections; however, the subsequent development of leukocytosis in the MP group was significantly greater at +6 hours. Rectal temperatures were higher in the MP group from +1 through +4 hours than in the controls. Hyperglycemia developed initially in both groups, followed by a progressive hypoglycemia, with survivors returning to near normal blood glucose concentrations. Hemoconcentration occurred in both groups, with higher hematocrits being associated with mortality. Results support the view that methylprednisolone sodium succinate does not affect the clearance of live E coli organisms.