[AS PER AMENDMENT 08/29/01: This study population will consist of infants from domestic sites and international sites.] In this double-blind, controlled study perinatally HIV-exposed infants less than 15 days old [AS PER AMENDMENT 08/29/01: "less than 15 days old" has been replaced with: less than 17 days old] at time of study entry are randomized to 1 of 2 arms to receive either concentrated formula or standard formula for 8 weeks after being stratified by gestational age: less than 37 versus greater than 37 completed weeks. At the 8-week visit using a previously determined 8:1 random allocation, 89% of singleton infants [AS PER AMENDMENT 08/29/01: from international sites] with negative HIV-specific tests are discontinued from study treatment and further follow-up. The other 11 percent of these singleton infants with negative HIV-specific tests continue study treatment with open-label standard formula until Week 28 (control group). Singleton infants with positive HIV-specific tests continue on the blinded portion of the study and receive formula as initially assigned until Week 28. For a given multiple birth, if any of the infants at the 8-week study visit are determined to be infected, all the infants from that birth continue their initial blinded treatment assignment until Week 28; if none of the infants are determined to be infected at this time, all the infants from that birth continue study treatment with open-label standard formula until Week 28. All infants assigned to receive study treatment through Week 28 continue study follow-up until 12 months of age. A subset of patients at sites with appropriate resources will participate in a substudy in which measurements of triceps and thigh skinfold thickness and circumference and thigh density DEXA scans are evaluated.