Maternal serum activin A levels are elevated in women with preeclampsia. To explore whether this could be due, at least in part, to increased production by the gestational tissues, we have measured activin A in the serum of women with (n=23) or without preeclampsia (n=62) at 29-40 weeks of gestation and in placenta and fetal membranes from preterm preeclamptic (PT-PE, n=8), term preeclamptic (T-PE, n=10) and healthy term controls (T-C, n=10). We have also explored if there are associated changes in activin receptor Alk2, ActRII and ActRIIB in these tissues. The relative amounts of receptor proteins were measured by densitometry on Western blots and receptors and activin beta(A) subunit localised by immunohistochemistry in PT-PE, T-PE and T-C gestational tissues (n=8-10/group). Maternal serum activin A levels were significantly elevated in women with preeclampsia (multiples of the normal median (MoM)=3.5, P<0.0001, Mann-Whitney U test) compared with healthy women (median MoM=1.0). Compared with control tissues, the activin A content was significantly higher in preeclamptic placentae (P=0.001 and P=0.0005 for PT-PE and T-PE respectively, Mann-Whitney U test), but significantly lower in the amnion (P=0.005 and P=0.014 for PT-PE and T-PE respectively) and choriodecidua (P=0.009 for T-PE). The maternal serum activin A level in women with preeclampsia was significantly correlated with elevated placental production (P=0.01, Pearson's correlation). Receptor Alk2 protein levels were significantly elevated in T-PE placentae (P=0.0006, Mann-Whitney U test), ActRIIB levels were significantly lower in PT-PE placentae (P=0.01) and ActRII levels were significantly lower in PT-PE choriodecidua (P=0.0002) compared with controls. There were no apparent differences in the distribution of the beta(A) subunit and receptors Alk2, ActRII and ActRIIB between control and preeclamptic tissues. These findings suggest that elevated levels of activin A in the maternal circulation in association with preeclampsia are due, at least in part, to increased placental production, and that the regulation of activin synthesis in placenta and fetal membranes is differentially regulated. Further, the differences in activin receptor protein levels between preeclamptic and control placenta and choriodecidua suggest that activin A-induced regulation may be altered in preeclampsia.