Our research interest is the study of some aspects of the genetics, genomic organization, and functionality in addition to molecular mechanisms involved in the parasitism of Leishmania. This organism is a flagellate-protozoan parasite and the ethiological agent of leishmaniasis, a disease that presents a wide range of clinical manifestations, from innocuous cutaneous lesions (CL) that can evolve to mutilation to the serious and sometime lethal visceral form (VL). The last two decades witnessed an increased prevalence of all forms of leishmaniases with an expanded incidence and geographical distribution, the disease is a serious public health problem in Brazil. The Leishmania Genome Project was implemented as an international consortium of laboratories and our group is part of this network. The activities within the network included the construction of a physical map for the entire genome and large-scale genome sequencing, which led to the complete sequence of a strain of an Old World species, the L.major. The relevance of biological information being gathered lies at the center of the matter. In this spirit we are currently studying some aspects of the parasite’s genome organization. We have as objects of interest, for instance, centromeric sequences and telomeric regions, for their relevance to the process of chromosome segregation or genetic plasticity of the parasite. We are also interested in comparative analysis of Old and New World species of Leishmania. In this direction, we are analyzing the genome of L.braziliensis, its organization and content comparatively to L.major. In addition, we study some factors and the mechanisms leading to the parasite virulence modification using reverse genetics. Finally, we are devoted to understand the role of transcripts of unknown function potentially involved in control of gene expression.