Thirty four canine biopsy specimens (lymph node, spleen, intestine and skin) with suspicion of malignant lymphoma were investigated in this study. Histopathological classification and B/T immuno-phenotypes were determined on the routinely processed formalin fixed, paraffin embedded tissue sections using rabbit anti-human CD3, mouse anti-human CD79a and rabbit anti-human kappa- and lambda-light chain as primary antibodies and streptavidin-biotin peroxidase complex procedure for immunolabelling. The T cell lymphomas (CD3 positive cells) constituted 61.5% (16/26) and B cell lymphomas (CD79a positive cells) 38.5% (10/26) of all immunostained specimens, whereas 8 cutaneous tumours with lymphoid-like lesions did not react with any marker of differentiation and could not be diagnosed as lymphosarcomas. Nodal and cutaneous lymphosarcomas were in majority T lymphomas (64.3 % and 62.5 % respectively) which 2 subtypes were identified based on histological criteria: non epitheliotrophic cutaneous T lymphoma in skin and T cell lymphoblastic lymphoma in lymph nodes and in spleen. Among the ten B lymphomas, 9 were positive for lambda and 1 for kappa light chain and 3 subtypes not associated with any specific tissue localisation were evidenced: B lymphocytic lymphomas (4/10), B lymphoplasmacytic lymphomas (4/10) and diffuse large B cell lymphomas (2/10). When considering the different subtypes, the 26 immunopositive neoplastic tissues consisted in 15.3% lymphocytic, 15.3% lymphoplasmacytic and 7.6% large cell B lymphomas whereas 19.2% and 42.3% comprised non epitheliotrophic and lymphoblastic T subtypes respectively. These results emphasize the interest of B and T immuno-phenotyping for the diagnosis of malignant lymphoma in dog.