 The histidine-rich protein II (HRP II) is a histidine- and alanine-rich, water-soluble protein, which is localized in several cell compartments including the parasite cytoplasm.The antigen is expressed only by "P. falciparum" trophozoites.HRP II from "P. falciparum" has been implicated in the biocrystallization of hemozoin, an inert, crystalline form of ferriprotoporphyrin IX (Fe(3+)-PPIX) produced by the parasite.