The acute systemic and neuropathologic effects ofE. coliendotoxin were determined in neonatal dogs. Administration of sublethal (LD0), moderate (LD50), or lethal (LD100) doses of endotoxin produced significant arterial hypotension, metabolic (lactic) acidosis, and hypoglycemia. Neuropathologic changes consisted of widespread inflammation in both grey and white matter; however, necrotic lesions were found only in forebrain white matter.