Spontaneous lymphoma is a frequently occurring disease in the canine species. These neoplasms are remarkably similar to their counterpart in humans with respect to histology, anatomic sites of involvement, and biologic behavior. In the present study, dogs with biopsy proven lymphoma were treated with total-body irradiation and objective remissions of disease were observed. A small group of patients with generalized lymphosarcoma have been treated concurrently with total body irradiation, and these preliminary clinical results are comparable to our experience with dogs. The increased exploitation of canine lymphoma as a model for experimental therapeutics is encouraged.