Abstract: The present invention relates to a method for detecting Borrelia burgdorferi sensu lato infection or the presence of antibodies against Borrelia species in a body fluid from a suspected infected or vaccinated human or other mammal, to a diagnostic kit useful in said method and to an immunoassay method for diagnosing early and late Lyme borreliosis, especially for diagnosing erythema migrans. The methods according to the invention are characterized in that recombinant BBK32 proteins, optionally other immunogenic borrelial proteins, or their fragments are used as antigens.