The immunocytochemical localization of insulin-like growth factor I (IGF-I) and platelet-derived growth factor A (PDGF-A) chain ligands, PDGF-chain receptors, and the intermediate filaments cytokeratin, desmin, and vimentin in the tissue reorganization and development during the establishment of the porcine epitheliochorial placenta was studied at light and electron microscopic levels in sections of endometrium and/or placenta of gilts during early pregnancy up to day 40 postmating. The endometrial epithelia (surface and glandular) as well as the trophoblast showed PDGF-A and IGF-I labelling. The only temporal difference was seen regarding IGF-I labelling, this being more uniform in the glands during precontact and early contact stages (days 7-12) compared to later stages. Cytokeratin labelling was conspicuous in all epithelia, including the trophoblast. The endometrial stroma showed strong labelling for the PDGF receptors and the intermediate filament vimentin, staining being enhanced along with the increase in the vascular bed during the establishment of the placenta. The maternal endothelium immunoreacted to IGF-I, to both PDGF-A and PDGF receptors, to vimentin and to von Willebrand factor (Factor VIII). Desmin was also expressed in the capillary bed underneath the maternal surface epithelium. In larger blood vessels, desmin was detected in the smooth muscle layer but not in the endothelium. The vascular smooth muscle also reacted with IGF-I, PDGF-A, and PDGF-receptor antibodies. The results suggest the involvement of both growth factors, IGF-I and PDGF, in the early nutrition of the pig embryo and the tissue reorganization that encompasses placentation. IGF-I appears to be related to the secretory tissue compartment (formation of histotrophe), whereas PDGF might play a role in the reorganization of the stroma, particularly during placental angiogenesis. Desmin and von Willebrand factor immunolabelling appears to be useful to monitor the development of the subepithelial capillary bed in the porcine placenta.