The present study correlated concentrations of activin A and follistatin in follicular fluid (FF) from human small antral follicles to FF concentrations of AMH, inhibin B, progesterone, and oestradiol and to the mRNA expression of FSH-receptor (FSHR), LH-receptor (LHR), AMH-receptor2 (AMHR2), CYP19a, and androgen-receptor (AR) in the corresponding granulosa cells (GC). FF from 144 follicles (3-12 mm in diameter) was included whereas mRNA expression profiles were established in GC from 66 of the 144 follicles. Levels of follistatin remained constant in relation to follicular diameter, whereas activin A levels increased in follicles exceeding 10 mm in diameter. Levels of activin A and inhibin B showed a highly significant inverse association. Follistatin showed highly significant positive associations with AMH and inhibin B levels and with FSHR and AR gene expression in GC. This study revealed unexpected associations that probably reflect the complicated regulatory mechanisms governing human folliculogenesis.