Systemic fungal infections in neonates are associated with high morbidity and mortality. The increasing use of intravenous central catheters, parenteral nutrition, and antibiotics in neonatal intensive care units has contributed not only to improved survival but also to the increasing incidence of fungal sepsis particularly in preterm infants. Decreasing fungal colonization can decrease the risk of systemic fungal infection. Fluconazole is a potent antifungal agent in the triazole family. Fluconazole has been shown to reduce the risk of fungal colonization and systemic infection however we do not have sufficient pharmacokinetic information in neonates to support dosing guidelines. In this study, we will perform a population pharmacokinetic study in neonates receiving fluconazole as standard of care. Fluconazole levels will be measured using a liquid chromatography/tandem mass spectroscopy (LC/MS/MS) assay from very small quantities of blood appropriate for neonates. Pharmacokinetic data obtained in this study will support appropriate dosing of fluconazole in neonates and provide information regarding drug metabolism in neonates.