We wish to obtain blood, urine, saliva, and stool specimens from healthy children ages 2-18 years for use in establishing the normal ranges of levels of hormones and the variations in genes that are important for hormones to act. Such hormone values are extremely important to allow endocrinologists to determine when hormone levels are truly abnormal in children suspected of an illness. Because the values of some hormones change with body size, we will obtain measurements of body composition when studying such hormones. Children participating in this study may be studied in the outpatient clinic (at most 2 blood draws) or as inpatients on the pediatric ward (for frequent blood sampling using an intravenous line over a 24-hour period). Other studies that may be performed as part of this study include ultrasound examinations of the thyroid, adrenal, ovaries or testes, and x-ray of the hand and wrist for bone age determination.