The uncleaved (one-chain) form of urokinase plasminogen activator associates with urokinase plasminogen activator receptor (uPAR), forming a complex at the cell surface (Cubellis et al. 1986). The complex is anchored to the outer face of the plasma membrane by a glycophosphatidylinositol moiety at the carboxy terminus of uPAR (Behrendt et al. 1990; Ploug et al. 1991).