This project funds the U.S. longitudinal study, which will follow a sample of breastfed babies more than 2 years (22 data points for each baby). The U.S. sample is essential if U.S. physicians and health care workers are to accept and use The World Health Organization (WHO) infant growth charts. The project is of particular relevance to WIC, which promotes the initiation and duration of breastfeeding. Current growth charts are based on surveillance data comprised mainly from formula-fed babies who are thought to have higher, though not necessarily optimal or appropriate growth rates for comparison with breastfed infants. The higher growth rate standards may lead health care workers to interpret the slower growth of breast-fed infants at about 4 months as indicative of growth faltering and erroneously recommend supplementation with formula or termination of breastfeeding. This could reduce the health benefits to infants associated with breastfeeding. A grant for $800,000 was awarded to WHO in fiscal 1998 to fund a U.S. site at the University of California, Davis for their international study to develop growth charts for healthy breastfed babies. In fiscal 2000 the grant was amended to include a cross-sectional component to measure children ages 18-71 months for reliable estimates of growth through the end of the 5th year of life. In fiscal 2001 a grant of $25,000 was awarded. The work is expected to be completed by December, 2002.