Following abdominal surgery and after sufficient washout from post-surgical analgesia, patients were randomized to one of the following four treatment groups; 1) oxymorphone IR 10 mg, 2) oxymorphone IR 20 mg, 3) oxycodone IR 15 mg, or 4) placebo. Total duration of treatment was 48 hours. Patients were required to take the study medication every 4-6 hours. After the first dose, periodic pain assessments were performed for the first six hours. Subsequently, patients were required to assess their current pain intensity and average pain intensity since the last dose of study medication just prior to every dose.