Because of the normal wide variability in timing and pace of puberty, standardized serial assessment of pubertal status of study participants will be performed to help distinguish between the effects of puberty and the effects of study treatments, increased age, height and weight on bone mineral accrual. Measurement of this variable is potentially of great importance in studies of children with chronic illnesses such as HIV-infection where delays in sexual maturation are common (de Martino 2001).