Multiple sclerosis (MS) is an idiopathic neurodegenerative, demyelinating disease of the central nervous system (CNS). MS affects females more than males (3:1) and pregnancy reduces the number of relapses especially during the third trimester when 17-beta-estradiol (E2) and estriol (E3) are at their highest levels. In order to study the role of estrogens as potential therapeutic agents for MS we investigated their role in Theiler's murine encephalomyelitis virus (TMEV)-induced demyelination (TVID). SJL female mice were infected intracranially with Theiler's virus or PBS. The mice in the treatment groups were clinically scored and at week 20 they were ovarectomized (OVx) and given a subdermal pellet containing either 1) 0.1mg of E2, 2) 5mg of E3, or 3) placebo. Four weeks after treatment initiation, the mice were sacrificed and tissue samples were collected and vertebral columns and brains were fixed and placed in paraffin for histological analysis using either hematoxylin and eosin (H&E) stain for general anatomic features or Weil's stain for myelin. No signs of clinical disease developed in any of the sham-infected mice. Prior to ovariectomy, infected mice had developed significant clinical scores indicative of demyelination. Mice in the placebo and E3-treatment groups deteriorated rapidly whereas the E2-treated mice improved significantly during the course of the treatment. Uteri were used to assess hormonal effects post-ovariectomy. Hormone treated groups were significantly different from placebo, indicating hormones were present. Hormone treatment showed significant differences among treatment groups for both inflammation and demyelination. E2-treatment significantly decreased inflammation compared to placebo and E3. E2 was also effective in reducing demyelination compared to placebo groups but not E3. E3 treatment was effective in reducing inflammation compared to placebo, but no significance was found for demyelination. Both E3 and E2 treated mice developed lower antibody levels against TMEV. The improvement in clinical signs, inflammation, demyelination, and the reduction of antibody levels in 17-beta-estradiol-treated mice indicate a therapeutic potential for the treatment of MS.