The situation in the chemotherapy of nematode infections. in both human and veterinary medicine, is currently satisfactory. There are different drugs available: the benzimidazoles, levamisole, pyrantel, and the different macrocyclic lactones (Tables 1. 2, 3, 4). In human medicine, mebendazole and albendazole are mainly used against the intestinal nematodes. while ivermectin and diethylcarbamazine are microfilaricidal drugs used in prophylaxis against onchocercosis and filarial infections. The situation in veterinary medicine is, however, governed by the great resistance problem in some animal hosts against all important anthelmintics. There are various reports of resistance against benzimidazoles, levamisole, pyrantel, and macrocyclic lactones in trichostrongylides in small ruminants (sheep, goats) and also Strongylides in horses. Resistance against ivermectin is now arising in cattle (Coles 2001; Sangster 2001). There are no reports of resistance problems in dogs and cats. Thus, there is always an urgent need in veterinary medicine for new anthelmintics with a new mode of action, which can easily break resistance against the existing anthelmintics. The situation in the chemotherapy of filarial infections in human medicine is not satisfactory. There is an urgent need for a new macrofilaricidal drug with only slight side-effects. Today, the only way is the prophylactic control of Onchocerca vovulus infections and treating lymphatic filariosis with ivermectin, diethylcarbamacine, ivermectin/diethylcarbamazine. or ivermectin/albendazole combinations.