Patients with infection, sepsis, severe sepsis, or septic shock were compared to each other and to healthy controls with regard to serum levels of biomarkers and clinical symptoms. Of the 15 biomarkers assayed, 9 were detectable in patients, and 4, in controls. Both proinflammatory and anti-inflammatory cytokines were detected in the patients. No single biomarker could differentiate the 3 septic levels of severity from each other; however, interleukin (IL) 1 receptor antagonist (IL-1ra) had the best sensitivity and specificity for differentiating sepsis and severe sepsis from septic shock. IL-6 was the only cytokine able to differentiate infected patients without signs of sepsis from those with sepsis. Although IL-1ra, IL-6, IL-8, and monocyte chemoattractant protein 1 could differentiate infection, sepsis, and severe sepsis from septic shock, the biomarkers could not differentiate sepsis from severe sepsis. The top scoring pair algorithm with clinical and biomarker analyses was able to correctly diagnose those with sepsis who will progress to a more severe state.