ISEE-191 Rationale: Di -2 -ethylhexyl phthalate is commonly used as a plasticizer in multiple medical products containing poly vinyl chloride and may represent between 20–40% of the finished weight of the plastic. Medical devices containing DEHP are in extensive use in modern NICU’s. The lipophilic nature of DEHP and its non-covalent binding to PVC allow it to leach from products being used. This is of concern, since in developing and adult laboratory animals, the metabolites have demonstrated multiple organ system toxicities, most notably hepatic and reproductive. We performed a cross-sectional study to assess the relationship of exposure to DEHP containing medical devices with internalized dose of DEHP in neonates as reflected by levels of MEHP (mono ethylhexyl phthalate) a principal urinary metabolite of DEHP. Methods: The study sample comprised (54) randomly selected infants enrolled nearly evenly from two Level III Boston hospital nurseries during the time period March 1– April 30, 2003. Subjects were in the NICU at least 3 days before observation, and had a corrected gestational age of ≤ 44 weeks. LOW, MEDIUM, and HIGH DEHP exposure classification categories were determined apriori, with the LOW exposure group containing subjects receiving primarily bottle and/or gavage feedings; the MEDIUM exposure group receiving enteral feedings, intravenous hyperalimentation, and/or nasal continuous positive airway pressure (CPAP); and the HIGH exposure group receiving umbilical vessel catheterization, endotracheal intubation, intravenous hyperalimentation and an indwelling gavage tube. Neonatal urine samples were collected from each infant using a standardized protocol and measured for MEHP by liquid chromatography (HPLC) and tandem mass spectroscopy (MS/MS). Results: MEHP levels tended to be greater among male infants and among infants with lower gestational age and longer stays in the NICU. MEHP levels were substantially higher with increasing exposure class: for the LOW, MEDIUM, and HIGH exposure classes, mean (sd) MEHP levels were, in ng/mL, 9.3 (9.8), 41 (55), and 139 (189), respectively (p=0.004, ANOVA of log-transformed values). Although further adjustment for institution and infant’s sex attenuated these differences somewhat (p=0.09), infants in the HIGH exposure class still demonstrated significantly higher MEHP levels than infants in the LOW exposure class (p=0.03). Conclusion: Use of DEHP-containing medical devices leads to demonstrable urinary levels of metabolites in NICU infants.