The maturation of T-cells depends on V(D)J recombination at the TCR α/β and γ/δ loci that occurs in the thymus during fetal development. Due to the essential role of the TCR β in thymocyte differentiation, it is important to define with precision the temporal emergence of the TCR β rearrangement and its expression in normal non-manipulated mouse strains. We studied the onset of the V(D)J recombination and transcription of the TCR Vα3 and Vβ11 genes during ontogeny in Balb-c, C57B1/6 and CBA inbred mouse strains. Our data show differences in the emergence of recombination in both TCR α and β loci among strains. The transcriptions of these loci followed respective recombinations and we detected an early germline transcript before TCR β locus recombination in the CBA strain.