Idiosyncracies are observed in captive wild animals as regards the pharmacokinetics and efficacy of anthelmintics. This could be attributed to such factors as differences in host's metabolism, irregular distribution of anthelmintics due to the way they are administered and worm resistance to anthelmintics. Previously mebendazole was found to be poorly effective when administered in feed. An experiment was conducted to evaluate the efficacy of mebendazole when administered at the dosage rate of 15-20 mg/kg body weight to gastrointestinal nematodes in captive gazelles. Fifty-eight adult gazelles (Gazella cuvieri) were divided into four groups: T1 (animals dosed orally, directly into the mouth), T2 (treated orally, mixed in the water of a herd), T3 (treated orally, mixed in the water of one animal), and T4 (not treated). Individual faecal samples were taken before treatment, and 15 days thereafter. Mean percentages of reduction of egg shedding were calculated for Nematodirus spp., other trichostrongyles, total trichostrongylids, Trichuris spp. and total nematodes. No statistically significant differences were detected between the treatment groups and the control group or among the animals in the three treatment groups.