Endostatin, the C-terminal fragment of the basement membrane protein collagen XVIII regulates epithelial cell migration and impairs tumour growth by inhibiting angiogenesis. Here, we investigated the expression pattern of collagen XVIII/endostatin in human placental and decidual tissues of various ages of gestation as well as in primary villous cytotrophoblasts, trophoblast cell lines, and villous explant cultures differentiating along the invasive pathway. RT-PCR analysis revealed production of collagen XVIII mRNA in total placenta and decidua of early and late pregnancy and in SGHPL-5 and HTR-8/Svneo cells. Collagen XVIII transcripts were absent from purified extravillous trophoblasts and syncytialising trophoblast cultures. Accordingly, an antibody against a protein domain common to different collagen XVIII isoforms detected the 180 kDa protein in villous and decidual tissue and cultivated placental fibroblasts but not in the different isolated trophoblast cell types. Immunohistochemical analyses localised collagen XVIII to villous basement membranes and to the endothelium as well as to placental and decidual stromal cells. Interestingly, expression of various forms of endostatin (20 and 26 kDa) was detected in placenta and decidua using Western blot analyses. Moreover, supplementation of recombinant endostatin increased MMP-2 expression in villous explant cultures and SGHPL-5 cells suggesting that the inhibitor may modulate extravillous trophoblast differentiation.