A comparative study of human sera was conducted to determine which purified preparations of 11 recombinant antigens of Borrelia burgdorferi sensu stricto were diagnostically most important in enzyme-linked immunosorbent assays (ELISAs). To assess sensitivity, 20 serum samples obtained 1-6 weeks after onset of illness from 20 persons who had physician-diagnosed erythema migrans (EM) were tested for IgM and IgG antibodies. In tests for IgM antibody, seropositivity of > or = 25% was recorded when ELISAs had separate preparations of protein (p) 37, p41-G, outer-surface protein (Osp) C, OspE, OspF or VlsE antigens. Sera reacted most frequently (80% positive) with VlsE antigen in analyses for IgG antibodies. When results of both class-specific assays were considered for VlsE, OspC or OspF, 90% of the EM cases were serologically confirmed. Results of specificity testing with a further 59 sera from persons who had syphilis, louse-borne relapsing fever, oral infections, rheumatoid arthritis or human granulocytic ehrlichiosis and 28 normal sera indicated no false positive reactions when VlsE antigen was used in tests for IgM antibody. One of the 11 louse-borne relapsing fever sera cross-reacted with VlsE antigen in tests for IgG antibodies. Minor cross-reactivity also occurred when p37, OspC, OspE or OspF antigens were used. Overall, VlsE was the most suitable antigen for laboratory diagnosis of Lyme borreliosis during the early weeks of B. burgdorferi infection because of its high sensitivity and specificity.