NCI is conducting a cross-sectional project exploring adrenarche as a critical period affecting reproductive hormone levels and potential links to breast cancer risk. Healthy girls aged 5-16 were recruited from four populations: 1) Bangladeshi sedentees still living in Sylhet, Bangladesh; 2) Bangladeshi first generation migrants to Britain; 3) Second generation Bangladeshis in Britain; and 4) British residents in similar communities. These populations were chosen because the developmental environment in Bangladesh differs greatly from that in the United Kingdom specifically with regard to economic factors, access to health services and exposure to infectious diseases. To determine developmental effects on puberty, investigators aim to compare androgen and estrogen levels among the four populations. A secondary aim is to explore whether immunological stress and/or diet influence the timing of and patterns of hormones associated with different stages of puberty.