['Administration of sc morphine has been recommended two hours after the end of iv morphine titration in the postanesthesia care unit (PACU), but in some cases patients complain of pain earlier than this. We assessed pain after the end of iv morphine titration and studied the characteristics of patients who needed rescue sc morphine.', 'Postoperative pain was assessed using the visual analogue scale (VAS; 0 to 100) and the threshold required to administer morphine in the PACU was a score of 30. VAS was measured every 15 min up to two hours after the end of iv morphine titration. Patients were divided into two groups, those who required sc morphine before two hours and those who did not. Data are expressed as mean +/- SD or odds ratio (OR; 95% confidence interval).', 'Four hundred and two patients were analyzed. Mean age was 51 +/- 19 yr, initial VAS 69 +/- 19, and the dose of iv morphine 11.7 +/- 6.6 mg. The number of patients requiring sc morphine within two hours was 84 (21%). These patients had more severe initial postoperative pain (73 +/- 20 vs 68 +/- 19, P < 0.05), and experienced sedation more frequently during morphine titration (45 vs 25%, P < 0.001). Using a multivariate analysis, occurrence of sedation during titration [OR 2.3 (1.4-3.8), P < 0.001] and an initial pain score > or = 60 [OR 1.9 (1.0-3.4), P < 0.05] were significantly associated with the need for rescue sc morphine.'] Are a high initial VAS score and sedation after iv morphine titration associated with the need for rescue analgesia?