The distribution pattern of fibronectin in the human placenta has been studied using the indirect immunoperoxidase (PAP) technique on formalin fixed paraffin embedded tissue samples. Fibronectin was demonstrated as intensely stained fibrillar or strand-like structures on the endothelial cells of blood vessels and on the amniotic epithelium. The most interesting fibronectin staining result, however, was found in the cytotrophoblast cells and in the bud-like structures of the syncytiotrophoblast. The results were discussed with regard to differentiation and proliferation in course of placental development.