This trial is designed to evaluate the effect of concentrated infant formula compared with standard infant formula on weight gain, growth and nutritional status in HIV-infected infants. The primary specific aim is to determine if caloric supplementation in HIV-infected infants, started within the first 14 days of life, results in improved growth as measured by weight or length at 28 weeks. The secondary specific aim is to a) determine the effect of nutritional supplementation on head circumference as an indicator of cerebral growth; immune status; opportunistic infection; and quality of life, and b) to evaluate the long term tolerability (28 weeks) of a concentrated formula compared to a standard formula in HIV-infected infants and the short term tolerability (8 weeks) of a concentrated formula compared to a standard formula in all HIV-exposed infants.