The lack of any parasite vaccine makes prevention against parasitic diseases to be based, as in the past, in ecological measures such as the environmental health and vector control to interrupt the biological cycle; on the other hand, it is also based in anti-parasite drugs. Once the disease has been acquired it is just possible to take medication. Studies on the way of action allow to understand more about the physiology of the parasite and, on the other hand, to understand better the physiology of the parasite allows to design new more effective drugs. However, the vast majority of these new drugs have been obtained thanks to intelligent and selective screening of generic molecules more than from the result of the knowledge of the biochemistry of the parasite. Despite all this, it is well known the mechanisms of action of many antiparasite drugs which have led us, when possible, to the discussion about possible targets to give an idea of how the rational approximation to design new medicaments is done.