One hundred seventy-six canine lymphomas were classified morphologically using four of the major human lymphoma classification schemes (Rappaport, Lukes-Collins, Kiel, and the Working Formulation). All 176 dogs received the same chemotherapeutic protocol. Sixty-two of these lymphomas had their immunophenotypes established by examination of cell surface markers by automated cytofluorography. Several different morphologic types of canine lymphoma were identified and these were comparable to morphologic categories in human classification schemes. Follicular and low grade lymphomas were rare. The two most common morphologic types were diffuse large cell (centroblastic) and immunoblastic. The Kiel classification appeared to be the most useful human scheme for classifying the canine lymphomas. Cytofluorographic analysis was generally straightforward, and 60 of the 62 lymphomas were placed into one of three immunophenotypic categories: 27 pan-T(LQ1)+SIg+, 21 pan-T(LQ1)-SIg+, and 12 pan-T(LQ1)+SIg-. Two of the lymphomas could not be characterized immunologically because a pre-existing or reactive non-neoplastic population of lymphocytes made interpretation of single cell suspension analysis difficult. The authors identified correlations between morphology and survival and disease-free remission; dogs with high-grade tumors generally survived the longest and had the longest remissions. No correlations were identified between high concentrations of serum lactate dehydrogenase, age, sex, or stage of disease, and morphology, immunophenotype, remission, or survival times. A significant correlation between clinical illness and survival time was documented. The median age of the dogs was nine years, no significant effect of sex on prevalence was observed, and some breeds were significantly overrepresented. Significant morphologic-immunophenotypic correlations included shorter remission and survival times for T-cell tumors than B-cell tumors, and a highly significant correlation between the pan-T(LQ1)+SIg-"T cell" phenotype and hypercalcemia.