OBJECTIVE To compare a technique of mechanical balloon declotting of thrombosed hemodialysis grafts with conventional pulsed-spray thrombolysis. METHODS Forty patients had 53 episodes of graft thrombosis over a 19-month period. Twenty-nine grafts were randomly treated with thrombolysis with urokinase and 24 grafts with mechanical declotting by placement of crossed balloon catheters within the graft. Patency was determined by retrospective review of hemodialysis records. RESULTS Successful hemodialysis for 1 week after the procedure was achieved in 21 (88%) of the 24 grafts treated mechanically and 26 (90%) of 29 grafts treated with thrombolysis. Continuous pulse oximetry showed no change in oxygen saturation in either group, and no clinical signs or symptoms of pulmonary embolism were noted. Average total procedure times were 2.2 hours for mechanical declotting and 3.5 hours for thrombolysis (P < .05). Probability of patency (mechanical vs thrombolysis) was 42% vs 45% at 3 months, 36% vs 25% at 6 months, and 8% vs 4% at 12 months. One major complication of ulnar artery embolization occurred in the thrombolysis group. CONCLUSIONS Mechanical declotting of hemodialysis grafts is faster and as effective as thrombolysis.