Recent studies have shown that narcotic druga produce an unusually intense, prolonged and segmental analgesic action in man when injected into the spinal subarachnoid or epidural space (Wang et al, 1979; Behar et al, 1979; Cousins et al, 1979; Magora et al, 1980, Johnston and McCaughey, 1980). Since 1960, many investigatora claimed that low molecular weight(LMW) dextran increased the clinical duration of lidocaine(Loder, 1960; Loder, 1962), tetracaine(Chinn and Wirjoatmadja, 1967) and bupivacaine(Kaplan et al, 1975) in man but the mechanism of the action of dextran was unclear. But Curtiss and Scurlock(1979), and Buckley and Fink(1979) claimed that LMW dextran has no effect on the duration of action of bupivacaine in animal studies. The present study was performed to evaluate the clinical efficacy of analgesia by the thoracic epidural injection of morphine and bupivacaine mixture for the relief of pain due to fractured or contused ribs, to evaluate the duration of analgesic effect by the use of the above mixture in a hypertonic solution(dextran 70 or 50% dextrose in water) and to observe the possibility of improvement in the lung function after the pain block. The complications following the pain block were also observed. The 50 single thoracic epidural injections of the mixture were divided into three groups: Group 1(n=15) served as a control group and drugs used for the relief of pain were as follows(Mean+/-S.D.): morphine(2.13+/-1.64 mg), 0.5% bupivacaine(3.10+/-1.04 ml) and 0.9% saline(3.64+/-1.11 ml). Group 2(n=16) served as an experimental group and drugs were as follows(Mean+/-S.D.): morphine(2.13+/-0.72 mg), 0.5% bupivacaine(3.06+/-0.77 ml) and dextran 70(3.75+/-1.29 ml). Croup 3(n=19) served as an experimental group and drugs were as followa(Mean+/-S.D.): morphine(2.42+/-0.51 mg), 0.5% bupivacaine(3.21+/-0.71 ml) and 50% dextrose in water(3.68+/-1.11 ml). The results are were follows: 1) The number of patients who obtained excellent and good analgesic effecta following the block were greater in the experimental Group 2(94%) and Group 3 (90%) than those of the control GrouP 1 (80%). 2) The duration of pain relief which lasted more than 3 days after the epidural block was longer in the experimental Group 2 (81%) and Group 3 (75%) than those of the control Group 1(67%). 3) The pulmonary reserve(FVC%+FEV1.0%) of 27 caaes who were treated by the pain block between 1 and 31 days following the chest injury was increased to about 13% than those before the block, and that of 13 cases between 32 and 82 days following the chest injury was decreased to about 4% than those before the block. 4) Of the complications following the pain block, there were 5 cases(10%) of nausea within 2 hours following the block, 4 cases(8%) of vomiting after 2 hours following the block, 10 cases(20%) of pruritus after 3-4 houra following the block, 17 cases(34%) of transient urinary retention which lasted 8 to 19 hours, 3 cases(6%) of headache within 2 hours following the block and 2 caaes(4%) of dural puncture. In conclusion, it is suggested that the clinical duration of analgesic effect produced by morphine and bupivacaine mixture can he prolonged by addition of the hypertonic solution to the mixture.