Abstract: The present invention relates to a generic capture ELISA for the detection and measurement of antibodies in biological fluids such as serum. This newly developed enzyme-linked immunosorbent assay (ELISA) system uses a first binding partner of a binding pair, preferably glutathione, crosslinked to casein as capture protein to bind recombinant protein antigens fused to a second binding partner of said binding pair, preferably N-terminal glutathione S-transferase (GST). The method not only allows the specific and efficient detection of antibodies in biological samples but, in addition, simple and efficient immobilization and one-step purificaton of overexpressed recombinant antigens even from crude lysates on ELISA plates coated with the first binding partner/casein. Several antigens can be tested in parallel under the same conditions without the need to biochemically purify or renature the proteins.