A 71-year-old man had sudden vision loss associated with headache. A temporal artery biopsy revealed a typical picture of giant cell arteritis. Subsequent steroid therapy failed to restore sight. A later blood culture contained spirochetes compatible with Borrelia species, and a silver stain of the temporal artery biopsy specimen demonstrated a similar spirochete. Treatment with i.v. ceftriaxone sodium led to some limited return of sight. To our knowledge, this is the first case report of a spirochete compatible with Borrelia found in a temporal artery biopsy specimen.