Ivermectin is a potent macro-cyclic lactone causing paralysis in many nematodes and arthropods through an influx of chloride ions across cell membranes. It is currently the drug of choice for human onchocerciasis and shows potent microfilaricidal activity against the other major filarial parasites of human (Wuchereria bancrofti, Brugia malayi, Loa loa and Mansonella ozzardi) but not against M. perstans. Whether or not it also kills the adult-stage of these parasites is currently under study. Ivermectin also has excellent efficacy in both human strongyloidiasis and cutaneous larva migrans for which good alternative treatments have not been available; and it is as effective as currently available drugs against the intestinal nematodes Ascaris lumbricoides, Trichuris trichiura and Enterobius vermicularis; against the human hookworms it shows only partial efficacy. Preliminary studies indicate that ivermectin has the potential to become the drug of choice for ectoparasitic infestations (mites, lice) of humans as well.