In order to examine the relation between breast development and hormone levels, serum levels of hormones including LH, FSH, PRL, progesterone, 17 alpha OH-progesterone, estradiol (E2), pregnenolone, pregnenolone-sulfate, 17 alpha OH-pregnenolone, cortisol, dehydroepiandrosterone (DHA), dehydroepiandrosterone-sulfate (DHA-S), testosterone and delta 4-androstenedione were measured by RIA in 162 puberal girls aged 9 to 17 years. Height and body weight were also measured. Stages of breast development were classified into B1 to B5 according to Tanner et al. Results were as follow; 1) Both body weight and height increased as the breast stage advanced during puberty. 2) The correlation with the concentration of hormone such as LH, FSH, E2, DHA, DHA-S and T, and breast development was noticed during the puberal stage before the onset of menarche. A significant positive correlation was observed between DHA-S, body weight and each stage of breast development before and after the onset of menarche. From the results obtained above, the intimate relationship between breast development and steroid concentrations especially the adrenal steroid DHA-S was suggested.