Inclusion Criteria

Children may be eligible for this study if they:

• Are 1 month to 12 years old.
• Are HIV-1 positive.
• Have not begun puberty.
• Are beginning or changing anti-HIV therapy and:
• (1) have never used anti-HIV drugs and are starting any anti-HIV therapy; or (2) have never used protease inhibitors (PIs) and are starting a PI-containing therapy; or (3) have used PIs in the past and are changing anti-HIV treatment and have never used at least 2 of the drugs in the new therapy.
• Have a parent or legal guardian able and willing to provide signed informed consent.

Exclusion Criteria

Children will not be eligible for this study if they:

• Have cancer.
• Use metal artificial body parts or electrical devices that have been inserted into the body (such as a pacemaker).
• Have had an arm or leg removed.
• Have a physical disability that would prevent an accurate measurement of body height or length.
• Have diabetes and need insulin.
• Have or have had a serious illness or fever in the 14 days before entering study (except an upper respiratory infection without a fever).
• Have used steroids (corticosteroids, anabolic steroids, or megestrol acetate), interleukin, interferon, thalidomide, or GH within 180 days before entering study. Glucocorticoids are allowed as long as treatment did not occur during the 14 days before entering study and total treatment in the 180 days before entering study was not more than 15 days.
• Have used anti-HIV medication, if they are beginning any anti-HIV therapy.
• Have used PIs, if they are beginning a PI-containing regimen. (Prior use of PIs is allowed if child is changing anti-HIV treatment and he/she has never used at least 2 of the drugs in the new therapy.)