In order to investigate molecular events involved in the regulation of lymphoid lineage commitment, we crossed lamda5 reporter transgenic mice to mice where the GFP gene is inserted into the Rag1 locus. This allowed us to sub-fractionate common lymphoid progenitors (CLPs) and pre-pro-B cells into lamda5-Rag1low, lamda5-Rag1high and lamda5+Rag1high cells. Clonal in vitro differentiation analysis demonstrated that Rag1low cells gave rise to B/T and NK cells. Rag1high cells displayed reduced NK-cell potential with preserved capacity to generate B- and T-lineage cells while the lamda5+ cells were B-lineage restricted. Ebf1 and Pax5 expression was largely confined to the Rag1high populations. These cells also expressed a higher level of the surface protein LY6D providing an additional tool for the analysis of early lymphoid development. These data suggest that the classical CLP compartment composes a mixture of cells with more or less restricted lineage potentials opening new possibilities to investigate early hematopoiesis.