1. A method of management of sheep at pasture is described which appeared successful in preventing reinfection by nematodes parasitic in the alimentary tract, with the exception of Strongyloides papillostts.2. A significant depression of liveweight gain was observed, due to a sub-clinical infestation in lambs at pasture.3. Reseeded pasture sown on land that had carried sheep 11 months before appeared to be worm-free.