• INCLUSION CRITERIA:

Volunteers will qualify for inclusion under this protocol if they meet the following criteria:

1. Good general health. Individuals with renal, hepatic, most endocrinologic (e.g. hypothyroidism, or Cushing syndrome), or pulmonary disorders (other than mild asthma not requiring chronic medication) will be excluded.
2. For obese subjects, body mass index for age above the 85th percentile (determined by NHANES I age-, sex-, and race-special data). For normal weight subjects of obese parents, body mass index (determined by NHANES I age-, sex-, and race- specific data) between the 5th and 85th percentile and both parents' current body mass index above 25 kg/m(2), or a history of a body mass index above 25 kg/m(2).
3. No significant psychiatric illness.
4. At initial visit, Tanner I (prepubertal) or Tanner II (early pubertal) pubic hair and breast stage of development for girls, and Tanner I or Tanner II pubic hair and testes size (6ml) for boys.
5. Subjects must be able to undergo MRI. Volunteers with metal in their bodies that are contraindications for MRI will be excluded. These include cardiac pacemakers, neural pacemakers, aneurysmal clips, shrapnel, ocular foreign bodies, cochlear implants, non-detachable electronic or electromechanical devices (such as infusion pumps, nerve stimulators, bone growth stimulators, etc.).
6. Age 6 to12 years at the start of the study.
7. For girls who have been followed to an age when they are menstruating (or are of an age when pregnancy is a possibility), a negative pregnancy test.
8. Race of all 4 grandparents self-identified either as all Caucasian or all African American.