Fibronectin has been found to bind metal ions. Using metal chelate chromatography and limited proteolysis to generate the distinct functional domains of fibronectin we set out to address the metal binding sites to well-defined regions of fibronectin. The results show that the affinity binding of fibronectin to Co 2 + is mediated exclusively via the collagen binding domain of the molecule, whereas fibronectin will bind to Zn 2 + , Ni 2 + , and Cu 2 + by metal binding sites located in two, three, and four well-defined regions of fibronectin, respectively. Fe 2 + and Mn 2 + chelates did not bind any of the isolated fibronectin domains. Combined metal chelate affinity chromatography opens a possibility to isolate particular fibronectin domains.