Twenty patients with tibial fractures had measurements of tissue pressure in the anterior compartment acutely and for the first 72 hours following injury. Measurements were made using a mercury monometric indicator similar to that described by Whitesides. Patients with fractures of the proximal third of the tibia, those with displacement of the fracture fragments greater than 50%, and those whose injury was the result of high-energy trauma developed higher compartment pressures and we conclude that such patients should be observed closely for the development of a compartment syndrome. In normotensive patients in this series fasciotomy was not necessary for tissue pressures less than 50 mm Hg in the absence of any sensory or motor compromise.