The anti-edema effect of edaravone, a free radical scavenger, was evaluated by magnetic resonance imaging in six patients with extensive hemispheric ischemic stroke. T(2) relaxation time in the infarct core, the boundary zone of the infarct, and the noninfarcted hemisphere were calculated, and T(2) mapping was performed before and after edaravone administration. Edaravone administration significantly decreased the mean T(2) relaxation time in the boundary zone of the infarct from 121.5 +/- 9.2 (mean +/- standard deviation) to 114.5 +/- 9.9 msec (p = 0.008), but not in the core from 142.3 +/- 13.4 to 142.2 +/- 18.5 msec (p = 0.97) or the noninfarcted hemisphere from 93.0 +/- 3.7 to 93.1 +/- 3.8 msec (p = 0.91). The T(2) subtraction map clearly demonstrated shortened T(2) relaxation time in the boundary zone of the infarct. The present results indicate that edaravone can salvage the boundary zone of the infarct and is a useful cytoprotective anti-edema agent.