In central and sub-Saharan Africa, the most important constraint to livestock production is trypanosomosis. This tsetse-transmitted disease is an important risk for about 60 millions cattle spread over 7 million km2. Several indigenous West African taurine (Bos Taurus) breeds, such as longhorn (N'Dama) or shorthorn (Baoule) cattle are known to control this trypanosomosis infection. This genetic capability named "trypanotolerance" results from numerous biological mechanisms most probably under a multigenic process. Amongst them are (1) the control of the trypanosome infection by parasitemia limitation and (2) the control of a severe anemia due to parasite pathogenic effects, both being the main criteria of trypanotolerance character. Till nowadays several methodologies did not succeed to identify the complete pool of genes involved in trypanotolerance. Nevertheless, new post genomic biotechnologies such as transcriptome analyzes are now efficient to characterize the full complement of genes involved in the expression of specific biological functions. One of them is the Serial Analysis of Gene Expression (SAGE) technique which consists in the construction of transcripts libraries for a quantitative analysis of the entire genes expressed or inactivated at a particular step of cellular activation. We develop this SAGE approach in comparing the total expressed genes during identical experimental Trypanosoma congolense infections in 2 trypanotolerant animals (one N'Dama and one Baoule) and one susceptible control animal (sudanese zebu). For each animal we develop 4 total mRNA transcripts libraries from blood white cells: one before experimental infection (To), one 48h after the parasitemia peak (Tp), one 48h after the PCV increase (Ta) and one at the end of the experiment (Tf). Firstly, for each animal we will compare the different activated and inactivated pool of genes at the different experimental stages. Secondly we will compare these results between the 3 experimenta