94 patients scheduled to undergo total hip arthroplasty were randomized to receive patient-controlled morphine paired with either intravenous metamizole or paracetamol as the postoperative analgesic regimen. The purpose of this study was to compare these two pharmacological interventions with respect to analgesic efficacy over the first 24 postoperative hours. Results indicated that patients in the metamizole group experienced significantly less pain and consumed significantly less morphine when compared to those in the paracetamol group. Patient sex, body weight and intraoperative blood loss were not significantly associated with postoperative pain in either study group. There was a significant negative correlation between patient age and postoperative pain in the paracetamol group only.