Lyme borreliosis is a tick-borne disease often manifesting as a circular skin lesion. This cutaneous form of the disease is known as erythema migrans. In a 5-year follow-up study in southern Sweden, 31 of 708 individuals initially diagnosed with erythema migrans and treated with antibiotics were found to be reinfected with Borrelia burgdorferi. Although men and women were tick-bitten to the same extent, 27 of the 31 reinfected individuals were women, all of whom were over 44 years of age. The aim of this study was to determine whether this discrepancy in gender distribution could be a result of differences in immunological response. Twenty single-infected and 21 reinfected women and 18 single-infected and three reinfected men were included in the study. None of the participants showed any sign of an ongoing B. burgdorferi infection, and thus the habitual response was captured. Lymphocytes were separated from blood and stimulated with antigens. The secretion of interleukin (IL)-4, IL-6, IL-10, interferon (IFN)-gamma and tumour necrosis factor (TNF)-alpha was measured by enzyme-linked immunosorbent assay (ELISA), enzyme-linked immunosorbent spot-forming cell assay (ELISPOT) or Immulite. No difference was detected in cytokine secretion between single-infected and reinfected individuals. We also compared the immunological response in men and women, regardless of the number of B. burgdorferi infections. Women displayed a significantly higher spontaneous secretion of all cytokines measured. The ratios of IL-4:IFN-gamma and IL-10:TNF-alpha were significantly higher in women. Gender differences in immune reactivity might in part explain the higher incidence of reinfection in women. The higher IL-4:IFN-gamma and IL-10:TNF-alpha ratios seen in women indicate that postmenopausal women have T helper type 2 (Th2)-directed reactivity with impaired inflammatory responses which might inhibit the elimination of spirochetes.