Patients undergo a corticotropin stimulation test within 8 hours of admission to the PICU. Blood samples for plasma cortisol and corticotropin levels are drawn at time 0 followed by corticotropin 1-24 IV. Additional cortisol levels are drawn at 30 and 60 minutes. Corticotropin is measured by immunoradiometric assay and cortisol is measured by radioimmunoassay. Mean arterial blood pressure, heart rate, and respiratory rate are recorded at baseline and at 60 minutes.