Third, we will monitor infants who are not receiving any enteral feeding at all for more than 4 weeks for any evidence of essential fatty acid (EFA) deficiency. Measurements will be repeated at the end of every 4 weeks that the subject remains without any enteral nutrition intake. Although the exact value suggestive of a deficiency is controversial, usually a level greater than 0.4 is considered evidence of EFA deficiency. This measurement may be made using 0.2 mL of serum in the lab of Dr. William Heird. Samples will be drawn monthly for infants who are NPO and run as a batch in Dr. Heird's lab in the CNRC every 6 months. Because data are not available for clinical use, we will include in the consent the possibility of EFA deficiency. We note again that no infant ever treated with Omegaven has ever shown clinical evidence of EFA deficiency, that very transient mild deficiency may occur in about 5% of infants and that there is no clinical intervention we would use in this case or that has ever been given without clinically apparent EFA deficiency.