Protein farnesylation is a form of posttranslational modification that occurs in most, if not all, eukaryotic cells. Inhibitors of protein farnesyltransferase (PFTIs) have been developed as anticancer chemotherapeutic agents. Using the knowledge gained from the development of PFTIs for the treatment of cancer, researchers are currently investigating the use of PFTIs for the treatment of eukaryotic pathogens. This "piggy-back" approach not only accelerates the development of a chemotherapeutic agent for protozoan pathogens but is also a means of mitigating the costs associated with de novo drug design. PFTIs have already been shown to be efficacious in the treatment of eukaryotic pathogens in animal models, including both Trypanosoma brucei, the causative agent of African sleeping sickness, and Plasmodium falciparum, one of the causative agents of malaria. Here, current evidence and progress are summarized that support the targeting of protein farnesyltransferase for the treatment of parasitic diseases. Parasitic diseases continue to have a major impact on morbidity and mortality in tropical and subtropical regions. Among these, malaria causes $300 million infections annually, with 1-3 million deaths occurring in Africa (1). The emergence and spread of parasites resistant to existing antimalarial agents is largely responsible for the recent increase in malaria-related mortality. Another reemerging disease is African sleeping sickness (African trypanosomiasis), with an estimated 50,000 deaths in 2002 (1). The increasing burden of these diseases, along with the inadequacies of current drugs for African sleeping sickness in terms of safety, efficacy, and ease of administration, have led investigators to seek new chemotherapeutic agents (2, 3). Among the current drug targets under study are enzymes involved in protein prenylation, or the posttranslational modification of proteins by the covalent modification by isoprenyl lipids, C15 farnesyl and C20 geranylgeranyl (4-7). The isoprenyl lipid modification of proteins has been shown to be critical for various cellular activities in mammals and yeast, including proliferation and apoptosis (8, 9). Growth of the protozoan parasites has been shown to be severely impaired by the inhibition of protein farnesylation compared with mammalian cells, suggesting high potential of the enzyme protein farnesyltransferase (PFT) as an antiparasitic drug target (5, 10-13).The isoprenoid synthesis pathway from mevalonic acid in many eukaryotes, including trypanosomatids (or deoxyxylulose in Apicomplexa, including Plasmodium and Toxoplasma, and plants) is essential for the production of sterols, dolichol, ubiquinone, and other isoprene derivatives in many eukaryotic cells. Indeed, these pathways have been the study of recent efforts to develop other antiparasitic chemotherapeutic agents, especially the targeting of isoprenoid pyrophosphate synthesis by nitrogen-containing bisphosphonates (14-16). Organisms belonging to the group Apicomplexa contain the nonmevalonate pathway of iso...