The present invention relates, e.g., to a composition comprising peptides represented by SEQ ID NO:1, or active variants thereof, wherein the peptides or active variants can bind specifically to an antibody induced by a causative agent of Lyme disease (a pathogenic Borrelia), e.g. in a sample from a subject having Lyme disease. Compositions of the invention may comprise multiple peptides, from multiple proteins. Diagnostic kits comprising the peptides are described, as are diagnostic assays using the peptides.