The recombination-activating gene 1 (RAG1) product is required for the somatic rearrangement of immunoglobulin and T-cell receptor genes. We cloned and sequenced the large continuous open reading frame coding for the salamander Pleurodeles waltl RAG1 protein. Semi-quantitative RT-PCR experiments were performed to quantify the expression of RAG1 in different tissues. The strongest signal was observed in the thymus of juvenile animals, confirming the primary lymphoid nature of that organ. Weaker expression was observed in the spleen, brain, and eyes of adults. Signals in these tissues represented 5.5%, 4.6%, and 2.0%, respectively, of the signal detected in the thymus. Expression in brain was confirmed by in situ hybridization. Similarly, low amounts of RAG1 transcripts were previously detected in the mouse brain. Moreover, the transcription of RAG1 begins as early as the neurula stages of development. These data suggest that the RAG1 protein could play a role in the central nervous system of vertebrates.