To compare the analgesic efficacy and tolerance of propacetamol and morphine, 80 patients in good clinical condition were included in a prospective, parallel, randomized double blind trial after elective surgery expected to elicit light to moderate postoperative pain. At the end of general anesthesia, 40 patients received 30 mg/kg propacetamol and 40 0.2 mg/kg morphine, as a 15-min intravenous infusion. The groups were similar for age, weight and duration of anesthesia. Supplemental analgesia had to be given in 7 cases from the propacetamol group vs. 2 cases from the morphine group. The postoperative pain, evaluated 7 times during 4 h from the end of infusion with a visual analog scale, revealed a modest advantage for morphine at 0.5 and 4 h (p = 0.05). The respiratory rate was slightly lower after morphine (p = 0.02). No significant differences were observed in blood oxygen saturation, blood pressure, heart rate, body temperature and vigilance evaluated by the trailmaking test. Nausea was present in 4 cases under propacetamol and 3 under morphine, and pruritus in 2 and 7 cases, respectively. In conclusion, propacetamol may represent an alternative to morphine for pain prevention after mildly to moderately painful surgery in situations where the use of opioids is unsuitable.