We originally suggested that calcium in the diet is important in determining the amount of bone (bone mass) that builds up in young adults. We are testing the effect of calcium on bone mass in 354 Caucasian (white) girls. At the start of this 7-year study, the average age of the girls was 11 years, and they had not yet reached puberty. The study will also provide information about the effect of calcium on body composition (body fat) and blood pressure in young women.