To investigate labour-associated changes in production of activin and related hormones by gestational tissues we prepared extracts from amnion, choriodecidual and placental tissues delivered at term before labour (TNL; n=15), at term after spontaneous labour (TSL; n=15) or preterm (PTD; n=31) and measured concentrations of inhibin A, activin A and follistatin by ELISA. Activin concentrations in placental tissues were significantly (Mann-Whitney U-test; P<0.05) elevated with term labour (pg/mg protein, median; 1313 vs 2591), but in the PTD tissues concentrations were lower than those delivered spontaneously at term (3650 vs 2649). Inhibin concentrations also increased with term labour in the placenta (480 vs 686), but paradoxically decreased in amnion (188 vs 64) and choriodecidua (657 vs 358). Little or no significant changes in follistatin concentrations were observed. Concentrations of all three proteins were significantly correlated between amnion and choriodecidual tissues, and were significantly correlated with each other in most tissues (Spearman's ranked correlation; P<0.05). The activin:inhibin ratio in term amnion and choriodecidual tissues was increased 2 to 3-fold (P<0.0005 by Mann-Whitney U-test) after term labour, with similar trends also observed in the activin:follistatin ratio in placental tissue. These data suggest that a modest increase in placental activin and inhibin production may occur with labour at term. In addition, an increase in activin bioactivity may occur with labour, potentiating any paracrine effects of activin during parturition. The data, however, do not support an association between increased intrauterine activin biosynthesis and preterm delivery.