To investigate the effects of sedation, anesthesia and surgery on lymphocyte blastogenesis, the administration of propionyl promzine and ketamine HCI and osteotomy of femoral head either alone of in combination were performed in dogs. Lymphocyte blastogenesis to the PHA-M stimulation was measured by counting $^3H-thymidine$ incorporated. Significant decrease of blastogenesis was observed until 72 hours after treatment in the group treated with propionyl proazine, but only at 4 hours in the group treated with ketamine HCI. In the group in which anesthesia and osteotomy of femoral head were performed blastogenesis decreased significantly until 24 hours after treatment. The present study indicated that transient depression of the lymphocyte blastogenesis after surgery was occurred due to the sedation and anesthesia as well as surgery itself.