Basement membranes of vascular endothelium, like those of other tissues, are composed of laminins, type IV collagens, heparan sulphate proteoglycans and nidogens. However, isoforms of all four classes of molecules exist, which combine to form structurally and functionally distinct basement membranes. The endothelial cell basement membranes have been shown to be unique with respect to their laminin isoform composition. Laminins are a family of glycoprotein heterotrimers composed of an alpha, beta and gamma chain. To date 5 alpha, 4 beta and 3 gamma laminin chains have been identified that can combine to form 15 different isoforms. The laminin alpha chains are considered to be the functionally important portion of the heterotrimers, as they exhibit tissue-specific distribution patterns and contain the major cell interaction sites. Vascular endothelium expresses only two laminin isoforms and their expression varies depending on the developmental stage, vessel type and the activation state of the endothelium. Laminin 8 (composed of laminin alpha4, beta1, gamma1 chains) is expressed by all endothelial cells regardless of their stage of development and its expression is strongly upregulated by cytokines and growth factors that play a role in inflammatory events. Laminin 10 (composed of laminin alpha5, beta1, gamma1 chains) is detectable primarily in basement membranes of capillaries and venules commencing 3-4 weeks after birth. In contrast to laminin 8, endothelial cell expression of laminin 10 is upregulated only by strong proinflammatory signals and, in addition, angiostatic agents such as progesterone. Current data suggest that laminin 10 contributes to the barrier function of endothelium, in particular to the extravasation of inflammatory cells. The data argue for a dynamic endothelial cell extracellular matrix that presents different molecular information depending on the type of endothelium and/or physiological situation.