The efficacies of nitroscanate and mebendazole against nematodes and Dipylidium caninum were compared by the examination of the faeces of 155 dogs. In unweaned puppies nitroscanate acted significantly faster and was significantly more effective than mebendazole against Toxocara canis. In adult dogs, both drugs had a low efficacy against Trichuris vulpis but a similarly good efficacy against other nematodes, with a tendency for nitroscanate to be more effective in reducing the prevalence of Ancylostoma caninum. Nitroscanate reduced the prevalence of D caninum infections considerably more than mebendazole.