How do animal hosts control worms? When an animal ingests an infective form of a gastrointestinal helminth (roundworm) from pasture, it can contain the infection by limiting the establishment, growth rate, fecundity and persistence of the parasite. This containment is achieved through the direct and indirect actions of the immune response. A helminth-specific immune response is, by and large, a local one and is achieved by an increase in the number of effector cells and the concentration of effector substances (such as specific immunoglobulins, proteases and mucin) in the gastrointestinal mucosa and lumen. The delivery of some of the effector substances is achieved through plasma leakage, part of which is irretrievably lost As these responses require nutrients for their expression and replenishment, it is not unreasonable to expect that host nutrition has the potential to affect the immune responses when nutrient resources are scarce. In this presentation we concentrate on the consequences of nutrition on the acquired immunity to parasites. Host nutrition can also affect innate immunity by, for example, making the gastrointestinal environment more hostile to parasites, but such effects will not be considered any further here.