The concentrations of AFP were evaluated in the sera from groups of healthy dogs and of dogs with multicentric lymphoma, before and while receiving chemotherapy. The concentration of AFP was highest in the affected dogs, especially during the fifth stage of lymphoma. Chemotherapy caused a decrease in AFP serum concentration, during both the induction and the maintenance phases of treatment, when compared to the same animals before therapy. Determination of the concentration of AFP in the serum may be an additional indicator in the evaluation of the stage of lymphoma, and of value in assessing the extent of neoplastic infiltration of the liver.