The adverse effects of pain in post-surgery or trauma patients are well documented. A reliable, safe approach to achieving unilateral analgesia in multiple contiguous thoracic dermatomes would be of great benefit to anesthesiologists in acute pain setting following thoracic or upper abdominal surgery. The aim of this study of post-cholecystectomy pain was to compare two methods of postoperative analgesia with interpleural block and paravertebral block with bupivacaine. Thirty otherwise healthy patients who had undergone elective cholecystectomy through a subcostal incision were randomly allocated to two groups of fifteen patients each and given either interpleural block(group 1) or paravertebral block(group 2) with 20 ml 0.5% bupivacaine mixed with 1:200,000 epinephrine through a single catheter. The degree of analgesia was assessed by a verbal rating scale, Prince Henry pain score and a visual analogue scale(VAS 1-10 cm ; O=no pain, 10=worst pain). These pain scores and vital signs were assessed just before and 10, 20, 30, 60 and 120 minutes after injection of bupivacaine. The onset time of analgesia was similar in both groups(6.6±3.74 minutes in group 1 and 5.5±2.88 minutes in group 2), but the duration of analgesia was significantly longer in group 1(6.5±1.92 hours) than group 2(4.5±2.17 hours)(p<0.05). In both groups Prince Henry pain scores significantly decreased 10 minutes after injection of bupivacaine and VAS also significantly decreased 10 and 20 minutes after injection(p<0.05), but there was no significant difference between two groups. The systolic blood pressure decreased 10 minutes after the injection of bupivacaine in both groups(Group 1-3.7%, Group 2-6.5%) and the diastolic blood pressure decreased 10 minutes after the injection of bupivacaine only in group 1(2.5%), (p<0.05), however, these changes in arterial blood pressure were of minimal clinical significance. There is no complication in group 1, but 2 out of 15 patients in group 2 showed bilateral blockade without any serious hemodynamic derangement clinically. In conclusion, both techniques showed similarity in the onset and the degree of analgesia except the duration of analgesia, and presented only a few minor complications. Therefore, we feel that paravertebral block can be used in case that coexisting pulmonary or pleural pathology limits the use of interpleural block for post-cholecystectomy pain management. Furthermore, either of the two techniques may be used alternatively in management of thoracic or upper abdominal pain according to technical skill and preference of anesthesiologists.