Our results show that following physical exercise to exhaustion, the levels of reduced glutathione are increased in the plasma, but decreased in both the liver and skeletal muscle of rats. Levels of glutathione disulfide are increased in all 3 tissues. Our results are consistent with a mechanism in which the liver may be dumping reduced glutathione into the plasma in an attempt to deliver it to those tissues that need it the most: in this case, skeletal muscle.