Experimental studies indicate that diesel exhaust can have deleterious effects on the CNS, including upregulation of the proinflammatory cytokine TNF-alpha [32] which can enhance motor neuron susceptibility to the excitotoxins [33] that are suspected to play a part in ALS [34], and upregulation of microglia [35] which also occurs in ALS [36]. This evidence concerns the gene TNF and amyotrophic lateral sclerosis.