Changes in energy metabolism in skeletal muscle tissue after high-energy trauma were studied. Trauma was inflicted to the thigh of anaesthetized pigs with a high-velocity missile. The changes in contents of adenine nucleotides, phosphoryl creatine, creatine, lactate and glycogen were studied within areas of discoloured muscle tissue nearest the wound and were compared with corresponding values in adjacent normally coloured muscle. Severe and presumably irreversible changes in energy metabolism were found in discoloured muscle, with depletion of ATP and phosphoryl creatine and marked increase in lactate levels. No such changes were found in the normally coloured tissue. The progression of the changes during a 10-hour observation period and the magnitude of the metabolic disturbance indicate that such discoloured muscle tissue must be regarded as non-viable. Discolouration can therefore be regarded as a useful clinical sign during debridement of traumatized muscle tissue.