It is believed that peak bone mass is a critical element in the determination of risk for osteoporotic fractures. During the period of peak mass there is a 1 SD black-white difference in bone mass which must contribute greatly to the 50% reduction in osteoporotic fractures among elderly black men and women in the U.S. This difference in peak bone mass must reflect processes which differ in black and white children during skeletal growth. This study will investigate: the black-white differences in rates of gain in bone mass in children aged 5-14; the relatioship between markers of skeletal turnover and rates of gain in bone mass in black and white children, and whether such differences account for differences in skeletal growth. Factors which might influence bone mass either through effects on skeletal modeling and remodeling during growth, or through other mechanisms, including sex steriods, growth hormone and other growth factors.