This study is the first to be performed in Amyotrophic Lateral Sclerosis (ALS) patients with the novel compound TCH346. Its purpose is to evaluate the safety and clinical effects of 3 dose levels of TCH 346 compared to placebo in patients with a clinical diagnosis of laboratory-supported probable, probable or definite ALS. The study will require patients to visit the study center a total of at least 7 times over the course of up to 14 weeks. The study consists of 2 phases: A screening phase (up to 2 weeks) when patients will be evaluated for eligibility to participate in the study, and a double-blind treatment phase (12 weeks) when patients will receive daily doses of either TCH346 or placebo and will be evaluated for clinical effects. In addition, patients eligible to participate in this study will be required to have 3 magnetic resonance spectroscopic (MRS) scans. The MRS is a non-invasive, painless, "brain scan". The MRS will require traveling to a designated center in Montreal, Canada, which is very experienced in performing such MRS scans in ALS patients.