Anti-dog tonsil rabbit serum was raised against New Zealand White Rabbit. This anti-serum was injected into three dogs and 12 hours later, the palatine tonsil, cervical lymph node and inguinal lymph node was removed out and histopathologic examination was done following the observation of the peripheral blood picture. Two dogs were used for control group. 1. Peripheral blood picture : Mean percentage decreased of lymphocyte was 72.4%, 50% and 48.4% in each case. While the total count of RBC and WBC were within normal limit. 2. Histologic findings : 1) Tonsil : Depletion of small lymphocytes was noted in the periphery of the follicle and in the perifollicular area. 2) Lymph node : Depletion of small lymphocytes were noted in the outer cortex paracortical area and cortico-medullary junction in all cases of anti-sera treated animals. No specific changes were observed in the peripheral blood and lymphoid tissues in control group.