Cell lines derived from spontaneous tumors serve as a research tool for cancer cell biology and new anti-cancer drug development. Isolation and propagation of canine lymphoma cell lines is difficult, thus only a few are available. Now we have established a new B-cell lymphoma cell line CLBL-1 from a dog with confirmed stage IV diffuse large cell lymphoma. Immunophenotyping of these CLBL-1 cells showed positive staining for CD11a, CD79alphacy, CD45, CD45RA, MHC II and cells were negative for CD3, CD4, CD5, CD8, CD11d, CD14, CD21, CD34, CD56 and T-cell receptor-gammadelta (TCR-gammadelta). PCR analysis for TCR-gamma and immunoglobulin heavy chain (IgH) gene rearrangements yielded a monoclonal result for the IgH gene. Furthermore, the clonality of IgH gene rearrangement was confirmed by sequencing of 16 positive bacterial clones. As canine lymphoma resembles non-Hodgkin"s lymphoma (NHL) in humans in many respects, this new cell line, will promote translational and comparative lymphoma research in humans and dogs.