>Magister Scientiae - MSc / Tsetse flies (Glossina spp) are vectors of African trypanosome (Trypanosoma spp) parasites, causative agents of Human African trypanosomiasis (sleeping sickness) and Nagana in livestock. Research suggests that tsetse fly immunity factors are key determinants in the success and failure of infection and the maturation process of parasites. An analysis of tsetse fly immunity factors is limited by the paucity of genomic data for Glossina spp. Nevertheless, completely sequenced and assembled genomes of Drosophila melanogaster, Anopheles gambiae and Aedes aegypti provide an opportunity to characterize protein families in species such as Glossina by using a comparative genomics approach. In this study we characterize thioester-containing proteins (TEPs), a sub-family of immunity-related proteins, in Glossina by leveraging the EST data for G.morsitans and the genomic resources of D. melanogaster, A. gambiae as well as A.aegypti.A total of 17 TEPs corresponding to Drosophila (four TEPs), Anopheles (eleven TEPs) and Aedes aegypti (two TEPs) were collected from published data supplemented with Genbank searches. In the absence of genome data for G. morsitans, 124 000 G.morsitans ESTs were clustered and assembled into 18 413 transcripts (contigs and singletons). Five Glossina contigs (Gmcn1115, Gmcn1116, Gmcn2398, Gmcn2281 and Gmcn4297) were identified as putative TEPs by BLAST searches. Phylogenetic analyses were conducted to determine the relationship of collected TEP proteins.Gmcn1115 clustered with DmtepI and DmtepII while Gmcn2398 is placed in a separate branch, suggesting that it is specific to G. morsitans.The TEPs are highly conserved within D. melanogaster as reflected in the conservation of the thioester domain, while only two and one TEPs in A. gambiae and A. aegypti thioester domain show conservation of the thioester domain suggesting that these proteins are subjected to high levels of selection. Despite the absence of a sequenced genome for G. morsitans, at least two putative TEPs where identified from EST data.