Enterovirus 71 (EV71), the newest member of Enterovirudae, is notable for its etiological role in epidemics of severe neurological diseases in children. It appears to be emerging as an important virulent neurotropic enterovirus in the upcoming era of poliomyelitis eradication, whereas no effective vaccine or antiviral agents are available at this moment. Human and bovine lactoferrins, iron-binding proteins belonging to the nonimmune defense system, were assayed in vitro to assess their inhibiting capacity on the cytopathic effect of EV71 on human embryonal rhabdomyosarcoma (RD) cells. Both bovine and human lactoferrins were found to be potent inhibitors of EV71 infection (mean IC(50), 10.5-24.5 microg/mL and 103.3-185.0 microg/mL, respectively). Lactoferrin probably exerts its effect at the level of viral adsorption, since the ongoing infection could not be further inhibited after the EV71 penetrated RD cells.