Amyotrophic Lateral Sclerosis(ALS) remains a terminal disease without an established etiology for the majority of patients. The dominant theory of ALS before the 1970’s was the presence of a poison. One of the primary means of treating patients with a toxic exposure has been plasma exchange, but plasma exchange of ALS patients failed to alter the clinical course. The failure of plasma exchange assumes the patient is no longer exposed to the poison. If the exposure to poisons continued, then plasma exchange alone would fail. I found laboratory evidence of a poisoning in every patient with ALS examined. A search for specific poisons found evidence of mycotoxins. Treatment with antifungal agents corrected the laboratory findings. All of the ALS patients had evidence of immune suppression. There is mounting evidence that many mycotoxins cause both neurotoxicity and immune suppression. These mycotoxins may be able to explain the full spectrum of pathology in ALS without a secondary event.