BACKGROUND: In spite of adverse reactions, morphine has been used as a basic constituent for patient controlled analgesia (PCA). Because morphine affects various immune functions, PCA with morphine may deteriorate immune mechanisms further after surgery. In this study we decided to determine how different is the morphine PCA from the combination of morphine and ketorolac in Interleukin-6 (IL-6) and IL-10 responses, analgesia and side effects. METHODS: Twenty two patients undergoing abdominal hysterectomy were randomly divided to two groups: PCA with morphine and PCA with the combination of morphine and ketorolac. Blood samples to measure cytokines were collected before induction of anesthesia, immediately after surgery, 1, 4, 24 h after PCA. Plasma was separated and frozen until the analysis of cytokines with ELISA. Postoperative pain was assessed using a visual analog score (VAS). Sedation was checked according to our protocol. RESULTS: In both groups IL-6 response rose immediately after surgery and stayed increased until 24 h, and IL-10 level peaked at 1 h after PCA then progressively declined. In the comparison of cytokines between the two groups there were significant differences in IL-6 at 24 h (P=0.026) and IL-10 at 4 h after PCA (P=0.03). In morphine consumption between the two groups there were significant differences (P=0.037 at 4 after PCA, P=0.015 at 24 h after PCA), however, pain scores, sedation and side effects were unaffected by the PCA regimen. CONCLUSIONS: We conclude that the supplementation of ketorolac with morphine modify the cytokine responses and in this way may contribute immune alterations during post-operative period.