Based on the good results of another author 10 boys with marked pubertal gynecomastia were treated with the antioestrogen Tamoxifen (Nolvadex) at a dose of 20-40 mg/d orally for 2-12 months. In most cases the gynecomastia decreased totally, only two patients experienced palpable subareolar glandular tissue at the end of therapy. Side effects were not noted. During therapy levels of estradiol and testosteron increased, with a more pronounced elevation of estradiol. Basal values of LH and FSH remained nearly unchanged, but LH showed an increased response to LH-RH, which could be explained by the antioestrogenic effect of Tamoxifen at the hypothalamic level. The reduction of breast size in spite of increased estradiol levels on the other hand, suggests that the mean therapeutic effect of tamoxifen is through estrogen receptor blockade of breast tissue.