A reliable screening assay for anti-interferon beta (IFNbeta) antibodies is needed for patients with multiple sclerosis (MS) receiving IFNbeta therapy. The performance of a new ELISA method, the capture ELISA (cELISA), was assessed by comparing it to a standard IFNbeta ELISA in correlating with neutralizing antibodies measurement in 453 sera from patients with MS. The cELISA outperformed the standard ELISA, and may be a suitable screening assay for anti-IFNbeta antibodies in IFNbeta-treated patients with MS.