BACKGROUND: Patient-controlled analgesia (PCA) is widely used for postoperative pain control. Theoretical advantages in maintaining an effective blood concentration of the analgesic medication using a basal infusion regimen is controversal. Therefore in this study, we compared the analgesic effect between PCA and PCA with a basal infusion and assessed whether the use of a basal infusion improves the analgesic effect in intravenous PCA or not. METHODS: Twenty six ASA physical status 1 or 2 female patients undergoing mastectomy were assigned randomly to the PCA group (group 1) or the PCA with basal infusion group (group 2). Group 1 was programmed to deliver 0.02 ml/Kg of bolus infusion with a 5 minute locKout interval. In group 2, 0.02 ml/Kg of basal infusion was added to the PCA regimen. The PCA analgesic solution contained 50 mg of nalbuphine and 150 mg of Ketorolac in a total volume of 200 ml. At sKin closure, 0.2 ml/Kg of a loading dose was given to all patients and a PCA was started according to the experimental group. A visual analogue scale (VAS) for pain, analgesic consumption, side effects and degree of satisfaction was assessed at postoperative 1 hour, 2 hours, 4 hours, 8 hours, 24 hours and 48 hours. RESULTS: Group 2 did not show any improvement in the VAS compared with group 1. Degree of satisfaction and incidence of complications were not different between two groups. Total infused amount of analgesics increased in group 2 (P < 0.05). CONCLUSIONS: The addition of basal infusion in a PCA after mastectomy did not show any improvement of postoperative pain control compared to the regimen of a PCA with only bolus infusion.