A protein (gal-FnBP), constructed by fusion of the genes encoding beta-galactosidase of Escherichia coli and the binding domains of fibronectin-binding protein (FnBP) of Staphylococcus aureus was used. FnBP is a surface protein responsible for attachment of bacteria to extracellular matrix of various host tissues. Gal-FnBP is more stable and can be produced in larger quantities than native FnBP. The binding specificity of this fusion protein was established in a Western blot analysis. Treatment of gal-FnBP with formalin inactivated the binding capacity of the protein but immunogenicity was retained. Immunisation of mice with formalin-treated gal-FnBP resulted in high antibody titres against the fibronectin-binding part of this fusion protein. These antibodies were measured by their ability to block the specific binding of fibronectin to gal-FnBP in a blocking assay. Sera raised against formalin-treated gal-FnBP and non-treated gal-FnBP blocked this binding to 40 and 25% respectively, thereby indicating the usefulness of gal-FnBP as a vaccine component.