The P2Y family of purinergic receptors are members of the G-protein-coupled receptor superfamily. The P2Y6 subtype is expressed at particularly high levels in the placenta, suggesting that P2Y6 plays an important role in placental function. However, the cellular localization of P2Y6 within the placenta is unknown. This study examined the expression of P2Y6 in first-trimester and full-term placental tissues, as well as examples of gestational trophoblastic disease, by Northern blot analysis and in situ hybridization. P2Y6 message was present at similar levels in first-trimester and full-term placenta, and in situ hybridization revealed that message was most abundant in the cytotrophoblast of the villi and chorionic plate at both gestational stages. The syncytiotrophoblast harbored lower levels of P2Y6 in first-trimester placenta, and by full-term, the syncytiotrophoblast only focally expressed P2Y6 transcripts. Neither the intermediate trophoblast nor nontrophoblastic elements of the placenta expressed P2Y6. Molar disease expressed P2Y6 in the villous trophoblast but not in the proliferative intermediate trophoblast, recapitulating the pattern of first-trimester placenta. Neither choriocarcinoma nor the choriocarcinoma cell lines JEG-3 and JAr expressed P2Y6 transcript. These findings reveal that P2Y6 mRNA production is highly characteristic of the epithelial-like cytotrophoblast and syncytiotrophoblast, whereas expression is absent in the mesenchymal-like intermediate trophoblast. Thus, P2Y6 may play an important role in trophoblastic development, differentiation, and neoplasia.