Inconsistent use of nomenclature in different canine malignant lymphoma (CML)classification systems, which lead to incorrect diagnosis and prognosis, necessitated a retrospective study of 103 cases of CML. Histological classification was done according to the Working Formulation, on H&E sections, after standard processing. Immunophenotyping, using CD3 (T cell) and CD79a (8cell) markers, was carried out on the same sections. Intermediate grade lymphomas were the largest category (49.5%), with 16.5%high grade lymphomas. More than half (53.3%) of the lymphomas were of 8 cell immuno phenotype, and 36.5% were T cell lymphomas. Only 9.7% of the total number of lymphomas exhibited double negative staining. Only two categories, the immunoblastic and medium-sized macro nucleolated (MMC) category (Fournel-Fleury et al.). exhibited constant (8 cell) immunophenotype. All the other categories exhibited mixed immunophenotype. The Working Formulation, with omission of the follicular tyoes (due to the rarity thereof in CML) and addition of the MMC category and immunophenotyping, is best for classifying CML. / Dissertation (MMed Vet (Pathology))--University of Pretoria, 1999. / Anatomy and Physiology / Unrestricted