Cytotrophoblasts are the specialized epithelial cells of the placenta. During the first trimester, a subpopulation of chorionic villas cytotrophoblasts differentiates along an invasive pathway and penetrates the maternal endo-metrium, decidua and spiral arterioles. Cytotrophoblast invasiveness declines rapidly during the second half of gestation. Isolated cytotrophoblasts of different gestational ages retain this differential invasiveness in culture. To determine whether the properties of integrin receptors for extracellular matrix molecules differ between invasive and non-invasive cytotrophoblasts, detergent extracts of isolated cytotrophoblasts of different gestational ages, and of first-trimester villous fibroblasts, were immunoprecipitated with subunit-specific anti-ηl integrin antibodies. Striking alterations in electrophoretic mobility were observed in η1 integrins from first-trimester cytotrophoblasts, as compared with those from term cytotrophoblasts or first-trimester villous fibroblasts, suggesting a cell-type-specific, temporally regulated alteration in glycosylation. Treatment of total first-trimester cytotrophoblast η1 integrins or the isolated α5/ηl fibronectin receptor with endo-η-galactosid-ase restored electrophoretic mobility to control levels, suggesting the presence of polylactosamine-bearing oligo-saccharides. Further analysis by enzyme digestion and lectin-affinity chromatography suggested that they consisted of at least three antennae and short, sialylated lactosamine units. These oligosaccharides did not affect the affinity of the first-trimester cytotrophoblast fibronectin receptor for fibronectin. However, this receptor bound more strongly to wheat germ agglutinin than control fibronectin receptor and resisted elution by high concentrations of sugar hapten, requiring ionic detergent for removal. These results suggested that the altered glycosylation affected the conformation of the fibronectin receptor.