Activin has been suggested to be an autocrine/paracrine regulator in the human placenta. In the present study, we examined the expression of the gene encoding activin type II receptor (ActRII) in this tissue. Using primers corresponding to the published sequence of human ActRII, a 456bp fragment was obtained from cDNAs prepared from the placenta, as well as the ovary and brain, by polymerase chain reaction (PCR). Southern blot hybridization of the PCR products and DNA cloning and sequencing confirmed that the product is the authentic ActRII. Trophoblast cells prepared from both first trimester and term placentae expressed the ActRII gene. When trophoblast cells from term placenta were separated into syncytiotrophoblast- and cytotrophoblast-enriched fractions and incubated for 1-6 days, ActRII gene expression was observed in both cell preparations, with the syncytiotrophoblast-enriched fraction having higher levels of expression at days 1, 3, and 4. These results provide the first direct evidence that the activin type II receptor mRNA is present in human trophoblast cells and strengthen the hypothesis that activin is an autocrine/paracrine regulator of placental function. To our knowledge, this is also the first report that the ActRII gene is expressed in the human brain and ovary.