60 children aged 3-10 years undergoing lower abdominal surgery will be randomized into 2 groups (30 patients in each group) to receive caudal block with bupivacaine (0.25%) 1mg/kg (group 1) plus tramadol 1mg/kg (group 2) just after the induction of general anesthesia without premedication. All children will be assessed for the post operative immune response by measuring interleukin 6 and 10 (IL-6 and IL-10) and Tumour Necrosing Factor-α (TNF-α) using enzyme-linked immunosorbent assay (ELISA) technique one hour preoperatively and three hours after incision.