A tibial fracture in the rabbit was used as a model of post-fracture swelling. A maximum increase in limb volume of 30 per cent was observed two to three days after injury. This swelling was significantly limited by an external pressure of ten millimeters of mercury applied by means of an air splint. On discontinuing the pressure, a "rebound" swelling was consistently observed, but nevertheless, the maximum swelling was dramatically reduced in the treated limbs when safe pressures were not exceeded.