My project consists in doing the analyses various genes encoding isoforms of the glyceraldehyde 3-phosphate-deshydrogenase (GAPDH) in protozoa. GAPDH is an enzyme of the glycolytic pathway, a very ancient energy-providing process, present in all living cells, from bacteria to animal cells. GAPDH is an excellent marker to study cell evolution at the molecular level because the various GAPDH isoforms are considered to originate from different primitive organisms, having given rise to the present day cells by an endosymbiotic evolution. Protozoa, specially the primitive ones, are very diverse in structure. They may represent different primary ways of cell construction and evolution from which the present animal and plant phylla originated. This aims to fill the gap in understanding the variety of protozoan organisms and from which type of organisms such primary cells originate.