The influence of sex hormones on the immune response to foreign antigens as well as self-antigens is now recognized. In this study, we investigated the influence of gender and sex hormones on the development of antibodies to double-stranded DNA in nonautoimmune C57BL/6J mice. Immunoglobulin G (IgG) anti-dsDNA antibodies are commonly present in lupus patients and several autoimmune disease-prone murine strains. We found that C57BL/6J mice have detectable antibodies (IgM and IgG, but not IgA) to dsDNA. Interestingly, the incidence and level of IgG anti-dsDNA antibodies were lower in male than in female mice. Orchidectomy or administration of 5 alpha-dihydrotestosterone to orchidectomized male mice had minimal effects on these antibodies. In contrast, administration of 17 beta-estradiol to orchidectomized or intact males significantly increased both the incidence and levels of anti-dsDNA antibodies. In female mice, ovariectomy decreased whereas administration of estrogen augmented the incidence and levels of anti-dsDNA antibodies in ovariectomized as well as intact female mice. Kinetic studies revealed that estrogen treatment of male and female mice induced earlier and sustained expression of IgG anti-dsDNA antibodies compared to controls. IgG subisotype analysis showed IgG2b to be predominant. In summary, our findings suggest that estrogen, but not dihydrotestosterone, promotes anti-dsDNA antibodies in normal mice.