Genes for the outer-surface protein C (OspC) from three north European human isolates of Borrelia burgdorferi sensu stricto, B. afzelii and B. garinii were cloned and sequenced. Polyhistidine-tagged recombinant OspC (rOspC) proteins were produced in Escherichia coli and used, after biotinylation, as antigens on streptavidin-coated plates in enzyme-linked immunosorbent assays (ELISA). In IgM ELISA, 30% (5/17) and 35% (6/17) of patients with erythema migrans (EM) in the acute or convalescent phase, respectively, reacted with one to three rOspCs. Of the patients, 53% (8/15) with neuroborreliosis (NB) and 53% (8/15) with Lyme arthritis (LA) had IgM antibodies to OspC. The immunoreactivity was stronger against rOspC from B. afzelii and B. garinii than against rOspC from B. burgdorferi sensu stricto. In early Lyme borreliosis (LB), rOspC and flagella performed equally well in detecting IgM antibodies. Cross-reactive antibodies to rOspC were observed in serum samples from patients with rheumatoid factor positivity and with syphilis or Epstein-Barr virus (EBV) infection. In IgM ELISA, thiocyanate in the serum dilution buffer reduced EBV-associated non-specific positive reactions. Of the patient sera examined in IgG ELISA, 30% (5/17) with EM in the acute phase, 35% (6/17) with EM in the convalescent phase, 33% (5/15) with NB and 60% (9/15) with LA were positive. Because of the heterogeneity of OspC, a polyvalent antigen with several OspC variants from at least B. afzelii and B. garinii is needed to improve the sensitivity of OspC ELISA in the serodiagnosis of LB in Europe.