Transcripts levels of superoxide dismutases increase slightly following infection of human dermal microvascular endothelial cells(HMEC-1) by the obligae intracellular bacterium Orientia tsutsugamushi, the causative agent of scrub typhus. In addition, fluorescence-activated cell sorter analysis demonstrates significant intracellular peroxide activity in infected cells within 5 hr after exposure to O. tsutsugamushi. Furthermore, infected cells experienced a significant depletion of glutathiones. These results support hypothesis that cells infected by this intracellular bacterium experience oxidant-mediated injury.