The molecular mechanisms regulating the cell fate decision between self-renewal and differentiation/apoptosis in stem and progenitor cells are poorly understood. Here, we report the first comprehensive identification of genes potentially involved in the switch from self-renewal toward differentiation of primary, non-immortalized erythroid avian progenitor cells (T2EC cells). We used the Serial Analysis of Gene Expression (SAGE) technique in order to identify and quantify the genome fraction functionally active in a self-renewing versus a differentiating cell population. We generated two SAGE libraries and sequenced a total of 37,589 tags, thereby obtaining the first transcriptional profile characterization of a chicken cell. Tag identification was performed using a new relational database (Identitag) developed in the laboratory, which allowed a highly satisfactory level of identification. Among 123 differentially expressed genes, 11 were investigated further and for nine of them the differential expression was subsequently confirmed by real-time PCR. The comparison of tag abundance between the two libraries revealed that only a small fraction of transcripts was differentially expressed. The analysis of their functions argue against a prominent role for a master switch in T2EC cells decision-making, but are in favor of a critical role for coordinated small variations in a relatively small number of genes that can lead to essential cellular identity changes.