The growth of lambs can be seriously affected by parasitic diseases, which may depend in part on the presence of worms in the animals' intestines. Various vaccines have been proposed to reduce worm infestation. An experiment was carried out to investigate these vaccines. For financial reasons, each vaccine was investigated by a fairly small experiment in which unvaccinated lambs acted as controls and vaccinated lambs formed the treatment group. Each lamb was injected with worms and then samples were taken some weeks later. The given data is for one vaccine only.