An experimental and clinical tehcnique of measuring tissue pressures within closed compartments demonstrates a normal tissue pressure is approximately zero mmHg, and increased markedly in compartmental syndromes. There is inadequate perfusion and relative ischemia when the tissue pressure within a closed compartment rises to within 10-30 mm Hg of the patient's diastolic blood pressure. Fasciotomy is usually indicated, therefore, when the tissue pressure rises to 40-45 mm Hg in a patient with a diastolic blood pressure of 70 mm Hg and any of the signs or symptoms of a compartmental syndrome. There is no effective tissue perfusion within a closed compartment when the tissue pressure equals or exceeds the patient's diastolic blood pressure. A fasciotomy is definitely indicated in this circumstance, although distal pulses may be present. The measurement of tissue pressure aids in the early diagnosis and appropriate treatment of compartmental syndromes.