Femoral medullary pressures and pulmonary embolization of medullary contents during the insertion of cement and a medullary rod in greyhounds were studied. In three animals, insertion of cement into the femoral shaft resulted in medullary pressures of between 290 and 900 torr and the appearance of medullary contents in the lungs within ten to 120 seconds. In five other animals, pulmonary embolization was not detectable when the rise in femoral medullary pressure was prevented by drilling a hole distal to the cemented area.