CONTEXT: Members of the Transforming-Growth-Factor-β (TGF-β) family have been implicated in aberrant follicle development in women with polycystic ovaries (PCO). OBJECTIVE: Are there quantitative differences in the concentrations of TGF-β family members in fluid from small antral follicles (hSAF) from women with or without PCO? DESIGN SETTING: & Follicle fluids (FF) were collected from 4-11 mm hSAF obtained from women undergoing ovarian tissue cryopreservation for fertility preservation. PATIENTS: FFs from 16 women with PCO (FF=93) and 33 women without PCO (FF=92). MAIN OUTCOME MEASURES: Intrafollicular concentrations of Growth-Differentiation-Factor-9 (GDF9), Anti-Müllerian-Hormone (AMH), inhibin-A and -B, total inhibin, activin-A, -B and -AB, follistatin, follistatin-like-3, estradiol, and testosterone. RESULTS: Activin-B concentrations are reported for the first time in hSAF and concentrations were 10 times higher than activin-A and -AB. Activin-B showed significant associations to other growth factors. Concentrations of inhibin-A and -B were significantly lower in FF from women with PCO, especially in hSAF below 8 mm in diameter. AMH concentrations did not differ between the groups in hSAF below 8 mm, however, AMH remained high in hSAF above 8 mm in PCO but decreased in non-PCO women. Estradiol was significantly lower in FF from women with PCO and showed significant associations with AMH. Concentrations of GDF9 are reported for the first time showing significantly higher concentrations in PCO FF of follicles above 6 mm. CONCLUSIONS: Altered concentrations of TGF-β family members in hSAF from women with PCO highlight altered growth factor signaling as a potential mechanism for follicle growth arrest.