In the assessment of viability of traumatized muscle tissue clinical signs, including colour, consistency, capillary bleeding and contractility have been commonly used. One of these signs, discolouration, has been shown in earlier studies to be associated with impaired circulation and severe and irreversible changes of muscle electrolytes and energy metabolism. In this study the circulation and tissue oxygen pressure fields were studied on either side of the "demarcation line" between discoloured and normally coloured areas of traumatized muscle tissue. Anaesthetized pigs were injured in one thigh with a high velocity spherical steel missile. The microcirculatory flow of the traumatized muscle was studied by measuring the clearance of 133Xenon from the surface of the muscle and tissue oxygen pressure (PtO2) was measured with an MDO electrode. Measurements were done before and 1, 3 and 5 hours after the trauma. A markedly decreased or absent flow as well as very low PtO2 values were found within areas of discolouration. In the adjacent normally coloured areas no such changes were noted and the values of these areas resembled those of the contralateral untraumatized leg. The results agree with those of earlier studies of circulation and metabolic changes indicating that discolouration is a useful sign in the clinical assessment of muscle viability after high-energy trauma.