Two patients with reinfection of Borrelia burgdorferi are presented. An 11-year-old girl developed recurrent acute peripheral facial palsy at an interval of five years. A 64-year-old woman showed paraesthesia in the leg and effusion in the knee. Three years later, an erythema migrans developed at the thigh. In both patients tick bites, corresponding clinical manifestations, and detection of specific antibodies proved the reinfections. The course of the humoral immune responses showed basic differences between the patients. At the interval between the first and second infection, the specific antibodies of the girl decreased beyond the cut-off level. On the other hand, the titer of specific IgG antibodies of the other patient remained at a constant level. Reasons for the failure of immune protection are discussed.