Inhibin B levels were measured in serum from 400 healthy Danish prepubertal, pubertal, and adolescent males, aged 6 -20 yr, in a crosssectional study using a recently developed immunoassay that is specific for inhibin B, the physiologically important inhibin form in men. In addition, serum levels of FSH, LH, testosterone, and estradiol levels were measured. Serum levels of inhibin B, FSH, LH, testosterone, and estradiol all increased significantly between stages I and II of puberty. From stage

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... I of puberty the inhibin B level was relatively constant, whereas the FSH level continued to increase between stages II and III. From stage III of puberty the FSH level was also relatively constant, although there was a nonsignificant trend of slightly decreased FSH levels at pubertal stage V compared to stage IV. The levels of serum LH, testosterone, and estradiol increased progressively throughout puberty. In prepubertal boys younger than 9 yr, there were no correlation between inhibin B and the other three hormones. In prepubertal boys older than 9 yr, a significant positive correlation was observed between inhibin B and FSH, LH, and testosterone. However, at this pubertal stage, each hormone correlated strongly with age, and when the effect of age was taken into account, only the partial correlation between inhibin B and LH/testosterone remained statistically significant. At stage II of puberty, the positive partial correlation between inhibin B and LH/testosterone was still present. At stage III of puberty, an negative partial correlation be-