The aim of this prospective study was to evaluate the efficacy of two dosage regimens of (i.m.) morphine calculated from an initial (i.v.) titrated dose in the early postoperative period. Seventy ASA I-III patients who underwent general anaesthesia (GA) (n = 58), regional anaesthesia (RA) (n = 10) or GA+RA (n = 2) for orthopaedic (n = 54), urological (n = 11) or abdominal surgery (n = 5) received i.v. titrated morphine in the post-anaesthesia care unit (PACU). Titration consisted of 3 mg morphine i.v. every ten minutes until patients had a visual analogue pain scale (VAS) < 3, without marked sedation. Seventeen patients did not complain at all or had good analgesia with an initial i.v. dose < or = 6 mg of morphine followed by paracetamol only. Patients who needed more than 6 mg i.v.morphine were randomly assigned to a "high-dose" or a "low-dose" group and received a systematic i.m. morphine regimen calculated from the initial titrated dose. Pain was assessed by VAS before each i.m. injection and the next morning. One patient had respiratory depression and one marked sedation in the PACU. These patients were excluded from the rest of the study. Only 16 patients were excluded from the rest of the study. Only 16 patients had a VAS > 3 at least once during the study period and only three needed rescue analgesia which was available on request. We conclude that a systematic i.m. morphine regimen adapted from an initial i.v. titration in the PACU provides efficacious and relatively inexpensive postoperative analgesia, applicable to a great majority of patients.