 Healthy girls under 6 years of age attending routine examinations including an i.v. line for other causes are included in this study. Our examinations also include bone age determination, Tanner stage determination, and anthropometric measures height and weight. 10 healthy girls in each of the following age groups: 7-12 months, 12-24 months, 24-36 months, 36-48 months, 48-60 months and 60-72 months are included. 