Placental fibrinoid is thought to contain various glycoproteins originating from cell secretion and tissue degeneration, occasionally merged with fibrin. Information on the characteristics and derivation of the various fibrinoid components, however, is still fragmentary. Therefore, the present histochemical study on acetone-fixed placental tissue sections compared the staining pattern of FITC-conjugated lectins from Ulex europaeus (UEA-I), Bandeiraea simplicifolia (BS-I) and Lycopersicon esculentum (LEA) with the reactivity of a fibrin antibody and a modified paraldehyde-fuchsin stain. Using different color reactions, the latter histological method identified two types of fibrinoid, which correlated well with fibrin-type and matrix-type fibrinoid. Immunohistochemically, fibrin was detected at the intervillous border of the basal plate, in some inner parts and in perivillous fibrinoid. UEA-I bound to endothelial cells and partially to fibrin-type fibrinoid of villi and the basal plate, thus indicating a reaction with immured and disintegrated remnants of endothelial and blood cells. LEA stained fibrin-negative (i.e. matrix-type) fibrinoid homogeneously within the basal plate; the small reactive areas within the perivillous fibrinoid may belong to degenerating trophoblastic residues, because in villi LEA specifically reacted with the syncytiotrophoblast. BS-I heterogeneously labeled matrix-type fibrinoid deposits in the basal plate which surrounded decidual cells and subpopulations of extravillous trophoblast. In cell islands, BS-I also stained fibrinoid surrounding trophoblast cells heterogeneously. The data (1) confirm the existence of two types of placental fibrinoid, fibrin-type and matrix-type fibrinoid, (2) suggest that both types of fibrinoid contain different glycoconjugates, and (3) demonstrate the practical usefulness of the modified paraldehyde-fuchsin method for the identification of the two types of fibrinoid.