To improve IgG antibody detection in the serodiagnosis of Borrelia burgdorferi infection, indirect enzyme-linked immunosorbent assays (ELISAs) were developed utilizing purified recombinant antigens of B. burgdorferi sensu lato: the chromosomally encoded proteins p100 of strain PKo (B. afzelii) and p4li (internal flagellin fragments) derived from strains PKo, PBi (B. garinii), and B31 (B. burgdorferi sensu stricto). In Western blot analysis, these proteins have proved to be highly specific and sensitive for IgG antibody detection, especially in late manifestations of Lyme borreliosis. Sera from 464 forest workers, a high-risk group for infections with B. burgdorferi, were investigated and the results compared with those obtained by a commercial ELISA using an octyl-beta-D-glucopyranoside (OGP) extract from B. afzelii (PKo) cells as the antigenic substrate. Sera derived from 200 blood donors served for determination of the 95% specific cut-off level. The number of positive test results using OGP-ELISA (23.9%) was only slightly higher than that using p100-ELISA (19.8%); corresponding results were observed in 84.7% of all sera (14.2% positive, 70.5% negative). The frequency and interassay correspondence of positive results increased with the age of the forest workers, as most markedly demonstrated by p100 and OGP assays (P < 0.0001). Using the p41i-ELISAs, generally no significant strain-dependent differences in sensitivity were found (PKo, 13.8%; PBi, 14.2%; B31, 12.9%). Compared with the p100-ELISA, the p41i-assays showed significantly lower detection rates for IgG antibodies (P < 0.03) and a reduced capacity for quantitative discrimination between seropositive individuals and negative controls (P < 0.0007). At a 95% specificity, the IgG antibody detection rate could be increased to 23.1% when the p100-ELISA was evaluated in combination with the assays using p41i/PBi and P41i/B31. Due to its high sensitivity, the specific recombinant p100-ELISA might be a suitable test for detection of late immune responses to B. burgdorferi, thus being especially useful for epidemiological investigations.