In the spring of 1932 an experiment was set up to observe the effects of intensive grazing, by the heavy stocking of a pasture, on the worm infestation of animals, and to arrive at some estimation of the consequences of modern grazing practices. These observations covered a period of one year and the results obtained from the experiment, which was carried out by one of us, have been put forward in an earlier paper (Morgan, 1933). Some conclusions were drawn from the work but these were considered as purely provisional owing to the small scale of the experiment and to the observations covering the comparatively short period of a year. It was pointed out that the effects of overstocking would not become evident until pastures had been under a system of rotational grazing for many seasons and when the concentration of helminth ova and larvae had reached a very high level. With this in mind it was decided to proceed with observations on the effects of heavy stocking on the worm burden by setting up a fresh experiment running on lines similar to that already described but using, in places of the goats in the 1932–33 work, one-year old sheep, as it was thought that this type of stock would ensure a closer cropping on the experimental plots.