The mechanisms underlying selective motor neuron degeneration in amyotrophic lateral sclerosis (ALS) remain unknown. There have been several important clinical trials on the treatment of ALS and treatment efficacy studies using mouse (SOD1) models of ALS. The latter revealed that diminished mutant SOD1 expression in the astrocytes delayed microglial activation and slowed disease progression. Dyslipidemia has been reported to have a protective effect in ALS patients. Current evidence has implicated a 43-kDa TAR DNA-binding protein (TDP-43) in the pathologenesis of ALS. Several mutations in TDP-43 were discovered in families with inherited motor neuron disease. Although phase III trials revealed that creatine monohydrate and IGF-1 was not beneficial for patients with ALS, favorable outcomes in SOD1 mice were reported with lithium, NADPH oxidase inhibitor, free-radical scavenger, and ammonium tetrathiomolybdate. Spinal and bulbar muscular atrophy (SBMA) is an adult-onset motor neuron disease affecting only males. Animal studies have revealed that the pathogenesis of SBMA depends on the serum testosterone level and that androgen deprivation mitigates neurodegeneration through inhibition of nuclear accumulation of the pathogenic androgen receptor (AR). Our studies have also identified several candidates for the treatment of SBMA. Selective inhibition of heat shock protein (HSP) facilitates the proteasomal degradation of pathogenic AR, leading to improvements in the signs and symptoms of SBMA mice. Oral administration of sodium butyrate--a histone deacetylase inhibitor--resulted in the improvement of neurological dysfunction in the SBMA mouse model, although its therapeutic dose range is narrow.