This is a global multicenter study designed to evaluate the safety and clinical effects of 4 oral doses of TCH346 (1.0, 2.5, 7.5, and 15 mg) compared to placebo in patients with mild or mild to moderate stages of ALS. The study consists of 3 phases: screening (up to 2 weeks), run-in (16 weeks), and a double-blind treatment phase of variable duration (at least 24 weeks).