Recent studios have shown that narcotic drags produce an unusually intense, prolonged and segmental analgesic action in man whoa injected into the spinal subarachnoid or epidural space (Wang et al, 1979; Behar et al, 1979; Cousins et al, 1979; Magora et a., 1980, Johnston and McCaughey, 1980). Since 1960, many investigators 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 Buckled 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 drags used for the relief of pain were as follows(Mean$pm$S.D.): morphine($2.13{pm}1.64;mg$), 0.5% bupivacaine($3.10{pm}1.04;ml$) and 0.9% saline($3.64{pm}1.11;ml$). Group 2(n=16) serves as an experimental group and drugs were as follows(Mean$pm$S.D.): morphine($2.13{pm}0.72;mg$), 0.5% bupivacaine($3.06{pm}0.77;ml$) and dextran 70($3.75{pm}1.29;ml$). Group 3 (n=19) served as an experimental group and drags were as follows(Mean$pm$S.D.) : morphine($2.42{pm}0.51;mg$), 0.5% bupivacaine($3.21{pm}0.71;ml$) and 50% dextrose in water($3.58{pm}1.11;ml$). The results are were follows: 1) The Dumber of patients who obtained excellent and good analgesic effects following the block were greater in the experimental Croup 2(94%) and Group 3 (90%) than theme 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 Croup 1(67%). 3) The pulmonary reserve(FVC%+FEV 1.0%) of 27 cases who were treated by the pain block between 1 and 31 drys 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 cased(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 hours following the block, 17 cases(34%) of transient urinary retention which tasted 8 to 19 hours, 3 cases(6%) of headache within 2 hoers following the block and 2 cases(4%) of dural puncture. In conclusion, it is suggested that the clinical duration of analgesic effect produced by morphine and bupivacaine mixture can be prolonged by addition of the hypertonic solution to the mixture.