A one-inoculation regimen of recombinant outer-surface protein C (OspC), which has been demonstrated to elicit protective immunity against a tick-borne challenge of Borrelia burgdorferi, was administered to outbred mice. Following seroconversion, the serum antibody titre against OspC was allowed to wane with time until there was little or no detection of anti-OspC antibodies by immunoblot. The mice were then challenged with an infectious dose of B. burgdorferi by tick transmission. Eleven of 12 OspC-primed mice subsequently became infected by B. burgdorferi, demonstrating that a protective anamnestic response was not generated in these mice following the introduction of infectious OspC-expressing spirochaetes.