We have previously described the use of the following recombinant antigens for serodiagnostic immunoblots: p83/100, p39, OspC and p41 (flagellin) internal fragment [Wilske et al. (1993) Med Microbiol Immunol 182:255-270; Rossler et al. (1997) J Clin Microbiol 35:2752-2758]. In our currently used immunoblot p83/100 is derived from strain PKo (Borrelia afzelii), p39 (BmpA) and OspC from strains PKa2 (B. hurgdorferi sensu stricto), PKo and PBi (B. garinii), respectively; the p41 (flagellin) internal fragments were cloned from strains PKo and PBi. In this study we describe the use of two additional recombinantly expressed highly immunogenic proteins Osp 7 (derived from PKo) and p58 (derived from PBi). A clinically well-defined panel of sera from 147 Lyme borreliosis patients and 139 controls previously tested by a standardized whole cell lysate immunoblot [Hauser et al. (1997) J Clin Microbiol 35:1433-1444] was investigated in the recombinant immunoblot without (old recombinant immunoblot) and with Ospl7 and p58 (new recombinant immunoblot) for IgG antibodies. The sensitivity of the recombinant IgG immunoblot for diagnosis of stage II and stage III could be significantly improved by addition of Osp17 and p58 without loss of specificity. With the exception of sera from patients with erythema migrans the diagnostic sensitivity is comparable to the whole cell lysate IgG immunoblot. The main advantage of the recombinant immunoblot is the easy identification of diagnostic bands, whereas the identification of bands in the whole cell lysate immunoblot is difficult. The recombinant immunoblot is especially suitable where large series of sera need to be investigated.