Through many contributing factors (ethnicity, diet, exercise, sun exposure, sex, etc.), bone density has traditionally been considered to reach a peak (PBD), during the third decade of life. More recently, data suggests this might occur earlier, mostly mediated by onset and duration of sexual maturation. In order to ascertain such contention, we studied 45 young (20-24 yr) adults utilizing single-photon absorption densitometry (SPA, Norland 2870), at the distal 1/3 of non-dominant arms, a site with 75% cortical bone. A uniform questionnaire on their life styles, ethnic/racial background, & biochemical/hormonal tests established their healthy state, as usually found among medical student volunteers. All had reached Tanner V stage. BD was obtained dividing BMC (bone mineral content, gm/cm) by BW (bone width, cm), and expressed as gm/cm2. Wt (weight) of Males (n = 24, age = 22.8 +/- 0.8 yr) was 77.9 +/- 8.9 Kg, height, (Ht) was 176.1 +/- 5 cm, both significantly higher than for Females (n = 21, Wt = 58.4 +/- 9.8 Kg, Ht = 159.2 +/- 5 cm), p < 0.0001). BMI (body mass index, kg/m2) were: M = 25.3 +/- 2.5 while F = 23.0 +/- 2.9 (p < 0.008). Ages were similar: M = 22.8 +/- 0.83, F = 22.5 +/- 0.81 years. Results were analyzed using SAS (IBM PS) & Cricket-graph (Macintosh), expressed as arithmetic means +/- SD or sem. LR (regressions) were applied whenever feasible.(ABSTRACT TRUNCATED AT 250 WORDS)