The complete gene sequence of a major phosphoprotein from the malaria parasite reveals that it is a homologue to cochaperone p23. This p23 homologue is highly conserved between Plasmodium falciparum and other malaria parasites and exhibits 44% sequence identity with the Schizosaccharomyces pombe p23 homologue. The Plasmodium p23 is a relatively abundant cytoplasmic protein with a molecular mass of 34-36 kDa depending on species. Expression of this 34 kDa protein and its mRNA commences in the early ring stage and continues throughout the trophozoite stage. At the beginning of schizogony there is a decrease in the transcription and translation rates and a decline in the amount of the 34 kDa protein. The exact role of the 34 kDa phosphoprotein in parasite replication and differentiation is not known, but the Plasmodium p23 homologue may play a role in parasite proliferation and differentiation through its interactions with protein kinases and other chaperones.