ABC proteins were first characterized in the protozoan parasite Leishmania while studying mechanisms of drug resistance. PGPA is involved in resistance to arsenite and antimonite and it most likely confers resistance by sequestering metal-thiol conjugates into an intracellular vesicle. PGPA is part of gene family with at least four more members which are in search of a function. Leishmania also contains a P-glycoprotein, homologous to the mammalian MDR1, that is involved in multidrug resistance. The ongoing genome project of Leishmania has pinpointed several novel ABC transporters and experiments are carried out to study the function of the ABC proteins in drug resistance and in host-pathogen interactions.