The aim of this study was to investigate the relationships between fasting serum ghrelin concentration, anthropometrical and body composition data in boys at different pubertal stages. Sixty healthy non-obese Estonian schoolboys (10 to 18 yr) were divided into 3 groups based on Tanner classification--group I was prepubertal, group II included stages 2 and 3, and group III stages 4 and 5. Additionally, we analyzed subjects as a total group. Fasting ghrelin, leptin, testosterone, insulin and glucose were collected between 08:00 and 10:00 h. Body fat % and lean body mass (LBM) were determined by dual-energy X-ray absorptiometry. Fasting ghrelin decreased, while leptin and insulin did not change and testosterone increased during puberty. There was a negative correlation between serum ghrelin and testosterone concentrations in group II (r=-0.51, p<0.05) and in the total group (r=-0.59, p<0.001). Ghrelin was also related to body height, body mass and LBM in group II and total group also with body mass index in total group. Stepwise multiple regression analysis showed that body height from auxological, LBM from body composition and testosterone from biochemical data explained 38.1, 41.7 and 33.7% of the ghrelin variance in the total group, respectively. In conclusion, body height, LBM and serum testosterone are the major determinants of serum ghrelin among parameters studied. Negative correlation between serum ghrelin and testosterone concentrations indicates that ghrelin may also have a role in male pubertal development.