First-stage larvae (L1) of the human hookworms Ancylostoma duodenale a
nd Necator americanus were frozen over liquid nitrogen after a 1-hr in
cubation in a cryoprotectant (10% DMSO and 10% dextran). Thawed larvae
developed to the infective third stage (L3) on agar plates. In the ca
se of A. duodenale, the larvae were infective to dogs. The infectivity
of N. americanus L3 was not tested.