The human hookworm Necator americanus was maintained through one hundred generations in the golden hamster (Mesocricetus auratus). The parasite strain employed here was ultimately adapted to hamsters without the requirement for exogenous steroids or other immunosuppressive agents. Moreover, there was no requirement to use neonatal hamsters--successful infections were obtained in 9- to 10-week-old hamsters infected subcutaneously with 250 hookworm larvae. This unique adaptation of N. americanus to hamsters permits its use for purposes of anthelminthic drug and vaccine development.