All infants in the Newborn Intensive Care Unit greater than three days old that had blood cultures sent were eligible for this study. Left-over blood from the time at blood culture was collected for research purposes. Study personnel separated the serum and stored samples at -80 degrees until analysis. Samples were analyzed in batch for neonatal sepsis biomarkers using an antibody-coated microsphere assay with dual laser detection. Clinical information collected included symptoms prompting the blood culture, CBC and culture results, and antibiotic therapy.