The present invention provides compositions and methods for treating ALS and other diseases, particularly motor neuron diseases that are mediated by aberrant aggregation of SOD. Patients with ALS may be treated using a compound of the invention which inhibits SOD aggregation mediated by a Cys-111 residue of SOD, or inhibits SOD aggregation mediated by labile SOD beta-barrel ends. The invention also provides methods for designing compounds capable of inhibiting aggregation.