Plasmapheresis means elimination of plasma and replacement of it with other liquids. Effect of this treatment is confirmed in more than 50 diseases like myasthenia gravis, Guillain-Barre syndrome and TTP. This cross sectional study was done on 25 myasthenia gravis patients referred to Shahid Sadoughi hospital, Yazd, Iran 2004-2007. We report 22 myasthenia gravis patients' response to plasmapheresis.