Faecal egg count patterns and clinical signs associated with gastro-intestinal (GI) nematodes of 107 zoo ruminants were monitored at fortnightly intervals for 1 year. The ruminants in this study were kept under different husbandry conditions at two sites of the Royal Zoological Society of Antwerp, the Antwerp Zoo and the Animal Park Planckendael. Artiodactylids involved were Arabian oryx (Oryx leucoryx), scimitar-horned oryx (Oryx dammah), bongos (Tragelaphus euryceros isaaci), sitatungas (Tragelaphus spekii gratus), common eland (Taurotragus oryx), impala (Aepyceros melampus), slender-horned gazelles, (Gazella leptoceros), blue wildebeest (Connochaetes taurinus taurinus), Kordofan giraffes (Giraffe camelopardalis antiquorum) and okapi (Okapia johnstoni). Nematode eggs were recovered from 586 of 1606 (36.5%) individual faecal samples, using flotation techniques. Infection levels were distinctly low at Antwerp Zoo, probably due to zero grazing and daily dung removal. At Planckendael, the herds of Arabian oryx, scimitar-horned oryx and slender-horned gazelles showed markedly higher egg counts than the other herds, with more than 10% of the faecal egg counts having more than 100 eggs per gram (epg) and maximum faecal egg counts of 600, 750 and 1350 epg, respectively. Faecal egg counts increased during the mid-grazing season (July) and peaked at the end of the grazing season (October). No clinical signs, such as loss of faecal consistency, could be correlated with faecal egg counts (P > 0.05). With the exception of significantly more Nematodirus spp. eggs that were present in juvenile eland, no differences in faecal egg counts could be found between the sexes and different age groups. Abomasa and intestines of 17 animals that died during the survey were available for total worm counts. In one Arabian oryx, four slender-horned gazelles and one sitatunga low burdens ranging from 200 to 14,300 were found. Nematode species recovered were Camelostrongylus mentulatus from the abomasa and Trichostrongylus retortaeformis, Nematodirus fillicollis, Capillaria spp. and Trichuris spp. from the intestines. Our findings suggest different nematode infection levels between herds, which are mainly due to husbandry conditions but to a lesser extent to species or individual susceptibility. Identification of ungulates that are highly infected and knowledge of the seasonal variation of their helminths can contribute greatly to a well-adjusted species-specific management and helminth control program.