The protozoan parasite Toxoplasma gondii has a worldwide distribution; it can cause serious diseases in humans and almost all other warm-blooded animals. Different genotypes of T. gondii result in different lesions in the same host. T. gondii rhoptry protein 8 (TgROP8) is a major factor of T. gondii acute virulence. We examined sequence variation in the TgROP8 gene among T. gondii isolates from different hosts and geographical localities. The TgROP8 gene was amplified from individual isolates and sequenced.