This paper provides, for the first time, comparative data on the plasma antioxidant status of two ruminant species, namely sheep and goats. In addition, the influence of experimental infection with Teladorsagia circumcincta on antioxidant status in the same two species is compared and contrasted. In general terms, antioxidant status was significantly higher in uninfected kids than in lambs. Differences in protein sulphydryl groups and vitamin E concentrations were particularly noteworthy; trends were similar, however, for albumin, vitamin A and total antioxidant capacity (TAC). Parasitological results, based on worm burden, faecal egg counts and peripheral blood eosinophil numbers, confirmed that goat kids were more susceptible than lambs to experimental T. circumcincta infection. "Trickle infection" had a variable impact on both total and individual antioxidant status; particularly during the early weeks, the trend was for reduced values in lambs and increased values in kids, as compared with uninfected controls. Subsequent challenge infection was associated with a transient decrease in TAC and albumin in trickle-infected animals of both species, and in appropriate control animals. The observed differences in plasma antioxidant capacity between sheep and goats may have important implications in terms of the comparative resilience of sheep and goats to parasite infection.