114 eligible subjects will be randomized to receive treatment for 6 months of (1) active creatine or (2) placebo. After randomization, subjects will be followed prospectively for 6 months. The primary outcome measure for the study is the change in upper extremity motor function after 6 months of experimental therapy as tested with the Tufts Quantitative Neuromuscular Exam. Strength in eight arm muscles will be measured (bilateral shoulder and elbow flexion and extension). Secondary outcome measures include grip strength, motor unit number estimates (MUNE), the ALS functional rating score-revised (ALSFRS-R), and rate of change of a well established biochemical marker of oxidative damage to DNA (8OH2'dG levels in urine), and the safety and tolerability of creatine.