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).

Inclusion criteria:

• clinical diagnosis of laboratory-supported probable, probable, or definite ALS;
• sporadic or familial ALS;
• ALS symptom onset for no more than 3 yrs at study entry;
• FVC equal to or more than 70%;
• patients who are either riluzole naive or patients who are receiving concomitant treatment with riluzole at a stable dose of riluzole (50 mg bid) at study start.

Exclusion criteria:

• Known or suspected chronic infectious disease including HIV, hepatitis B, or hepatitis C.
• Clinically significant ECG abnormalities.
• Known hypersensitivity to study drug or related drugs (e.g. selegiline, MAO-A and B inhibitors, or tricyclic antidepressants).
• Patients treated with potent inhibitors of CYP1A2 or CYP3A4 (a list of such inhibitors will be provided to the investigator).
• Treatment with MAO-A and B inhibitors (including selegiline) within the past 30 days.