 The study design will be a prospective observational study of patients presenting to the Memorial Hermann Hospital Emergency Department with sepsis. Criteria for sepsis include evidence of systemic inflammatory response syndrome as defined by the ACCPSCCM Consensus Conference, and a known or suspected infection. Exclusion criteria include signs of severe sepsis or septic shock, as defined by the ACCPSCCM Consensus Conference, at presentation, including: organ dysfunction, hypoperfusion and perfusion abnormalities. Chronic medical conditions associated with immune suppression or coagulopathies, such as neutropenia and sickle cell disease, and use of medications leading to immune dysfunction or coagulopathies, such as chronic steroid use or anti-coagulation will also be reasons for exclusion. In addition, because of the volume of blood required from each patient for laboratory studies, only patients 25 kg body weight or more will be enrolled. Withdrawal from the study will be at the discretion of the treating physician or subject. All efforts will be made to collect clinical information from patients who have withdrawn. 