Background. Serum leptin levels are strongly correlated with body fat, and increases in these levels precede rises in serum sex hormones in girls. Because African-American girls are heavier, taller, and mature earlier than Caucasian girls, we hypothesized that the serum leptin level might differ between the two groups.

Methods. Serum leptin concentrations were measured by immunoassay in 12-h fasted blood samples collected from 79 Caucasian and 57 African-American girls between 8 and 17 y of age. Body composition was measured by dual energy x-ray absorptiometry, sexual maturity by physical examination, and physical fitness by treadmill testing.

Results. Serum leptin concentrations were positively correlated(p < 0.01) with maturation and body fatness, and were higher (4.4 ng/ml, p < 0.01) in the African-American girls after controlling for differences in age, sexual maturity, fat mass, body weight, and physical fitness.

Conclusion. Serum leptin levels are higher in African-American girls than in Caucasian girls. The higher serum leptin levels might contribute to the earlier onset of puberty and accelerated growth in African-American girls when compared to Caucasian girls.