A total of 157 dogs with lymphosarcoma were available for study; 67 were treated. All of the treated dogs were given 4 drug combinations and 20 of them also were given autogenous vaccine. Sixty (90%) of the dogs treated with multiple drugs improved clinically. Of the dogs with clinical improvement, 48 (80%) had either complete or partial remission; of these, 32 (67%) had complete remission. Clinical staging proved useful in increasing the accuracy of prognosis, whereby dogs in less advanced stages of disease responded better to therapy, with a higher percentage of complete clinical remissions and longer survival. The mean survival time of the 47 dogs treated with drugs alone was 138 days, which compared with a mean survival time of 30 days for 34 nontreated dogs. Dogs subjected to chemotherapy and immunotherapy had a mean survival time of 341 days. Dogs in complete remission at time of vaccination survived significantly (P less than 0.01) longer than did dogs treated with drugs and vaccinated while not incomplete remission.