Objective To evaluate inhibin B and luteinizing hormone (LH) levels in a large, representative cross-sectional sample of US girls and characterize the relationships of these laboratory values with age, clinical signs of puberty and other correlates. Design Cross-sectional analysis of LH and inhibin B in banked serum from 720 girls aged 6-11 years who participated in the Third National Health and Nutrition Examination Survey (NHANES III). Measurements Levels of inhibin B and LH, race, ethnicity and anthropometric measurements were compared for all girls. Visual assessment of pubertal stage was performed on girls aged 8 years and older. A two-part model was used to establish normative data and Tobit regression models were used to evaluate associations with participant characteristics. Receiver operating characteristic (ROC) analysis was performed to identify optimum cut points predictive of puberty onset. Results Mean hormone levels progressively increased with age. LH levels progressively increased with pubertal stage. Inhibin B levels increased gradually from breast stage I to II, then more sharply to peak at stage III, followed by a plateau at stages IV and V. ROC curves indicated that both hormones were consistent with pubertal onset as indicated by breast stage II. Conclusions This study characterizes inhibin B and LH values in a large, representative cross-sectional sample of US girls. Inhibin B can be a useful tool in combination with other clinical and biochemical parameters to evaluate gonadal function as a reflection of pubertal progression in girls.