The authors rarely encountered slight cyanotic changes in patients who were given continuous epidural anesthesia with marcaine. Studies for clarifying the causal factors suggested that the occurrance of cyanosis was related to the formation of methemoglobin by continuous epidural anesthesia with marcaine. In these studies, as control, the blood was drawn before injection of local anesthetics by using a heparinized syringe and later the blood samlpe was obtained at interval one hour during epidural anesthesia and postoperative period. Quantitative assay of methemoglobin was carried out by the Evelyn-Malloy method using a spectrophotometer. THe result was that methemoglobin concentration in the peripheral blood after use of marcaine using increased compared with the controls. An animal experiment, rabbit was done and marcaine was injected in the gluteal muscle, revealed same result of human. In the studies of ascorbic acid pretreatment in the human, the authors pretreated with ascorbic acid via the intravenous route before epidural anesthesia and in the rabbit, ascorbic acid was injected into the gluteal muscle before injection of marcaine. THe increase of methemoglobin content in the blood appeared to be lesser with pretreatment of ascorbic acid in the patients who were given continous epidural anesthesia with marcaine. It is a recommendable method for reducing mothemoglobin be prior use of ascorbic acid in case of the regional anesthesia with marcaine(Bupivacaine, LAC-43) is used.