We have used Surface Plasmon Resonance (SPR) - based biosensor technology to investigate the interaction of the six high affinity insulin-like growth factor binding proteins (IGFBP 1-6) with the cell binding domain (CBD) of fibronectin. Using a biotinylated derivative of the ninth and tenth TypeIII domains of FN (9-10FNIII), we show that IGFBP-3 and -5 bind to FN-CBD. We show that this binding is inhibited by IGF-I and that, for IGFBP-5, binding occurs through the C-terminal heparin binding domain of the protein. Using site-directed mutagenesis of 9-10FNIII, we show both the "synergy" and RGD, sites within these FN domains are required for maximum binding of both IGFBPs. We discuss the possible biological consequences of our results. (C) 2009 Elsevier Inc. All rights reserved.