Currently used antiparasitic drugs, including benzimidazoles, nitroimidazoles, avermectins, polyene ionophores, hydroxynaphthoquinones and sesquiterpene lactones, were identified through the empirical route to drug discovery. The modern rational approach to drug design is focused upon the structure and function of biochemical and molecular targets. The requisite pharmacological properties for new anti-parasite drugs should not be ignored in this process.