Activin A is a dimeric protein composed of two beta A-subunits protein of the transforming growth factor-beta (TGF-beta) family. This protein is synthesized by a variety of organs. A sensitive and specific assay for bioactive dimeric activin A has recently been developed, to measure circulating levels in adult women and men, giving a new insights into the possible physiological role of this protein in the reproductive axis and/or in other functions. The aim of the present study was to evaluate serum dimeric activin A levels in boys and girls during pubertal development. The study was performed on a group of children (n = 54) aged between 6 and 18 years at different Tanner stages. Serum levels of activin A were measured using a specific and sensitive two-site ELISA. Serum activin A levels were not significantly different at various Tanner stages (Tanner I, 0.36 +/- 0.02 ng/ml; Tanner II, 0.33 +/- 0.02 ng/ml; Tanner III, 0.35 +/- 0.03 ng/ml; Tanner IV, 0.41 +/- 0.04 ng/ml; Tanner V, 0.35 +/- 0.05 ng/ml; p > 0.01). No difference between male and female children was observed. In conclusion, the lack of significant differences in activin A serum levels according to the Tanner stages or to gender demonstrates that this protein is not involved in the endocrine modifications during pubertal development and that its measurement may not provide a sensitive new tool for determining gonadal maturity at puberty.