High-voltage electrical burns are associated with deep muscle injuries. A hidden, deep muscle injury has no specific clinical manifestations, and undetected muscle injury sometimes leads to septisemia or major amputations. From January to December 1996, 52 burned patients were admitted to the burn center. We evaluated their laboratory findings and the results of diagnostic tools. The items of study were urine, EKG, CK-MB, CPK, LDH, SGOT, SGPT, PYP scanning, Plethysmography, and arteriography. The presence of myoglobinuria and the increase in SGOT and SGPT two weeks after the injury were related to the extent of the burns. The PYP scanning was a very sensitive and useful tool for detecting hidden muscle injuries. The arteriographic findings were unsatisfactory for deciding the amputation level. The PCR findings converting to obstructive type were helpful in predicting possibile amputations.