The effect of low dietary zinc on the survival of an intestinal nematode (Heligmosomoides polygyrus) was investigated in two experiments. In experiment 1 (primary infection), outbred CD1 mice were infected once only with 100 H. polygyrus larvae. In Experiment 2 (challenge infection), mice were given a primary infection that was terminated after 9 d using an anthelmintic drug; the mice were reinfected 5 d later. This protocol stimulates host immunity to the second parasitic infection. Three dietary treatments (control, 60 mg Zn/kg diet; zinc-restricted, 5 mg Zn/kg diet; and energy-restricted, 60 mg Zn/kg diet) were used for both experiments. Both infected and uninfected mice were included within each dietary treatment to control for the effect of parasitic infection on host nutritional status. Plasma zinc concentrations were significantly lower in mice fed the zinc-restricted diet, compared with mice fed the control or energy-restricted diets in both experiments; there were no significant differences in plasma alkaline phosphatase activity or tissue zinc concentration. The significant reduction in plasma zinc had no significant effect on worm burden or egg production of H. polygyrus in either experiment, indicating that the 30-40% reduction in plasma zinc was not sufficient to modify parasite numbers. However, the parasite did affect host nutritional status. Spleen weight was significantly higher in infected mice in both experiments. Following the challenge infection, both liver and spleen copper concentrations were significantly higher, and spleen iron concentration significantly lower, in the infected compared with the noninfected mice.