Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by loss of motor neurons in the spinal cord, brainstem and motor cortex. Ten percent of the cases are familial and these have been linked to point mutations in the gene coding for cytosolic copper, zinc superoxide dismutase. The etiology of sporadic ALS is unknown. To further investigate the possible role of metals in causing the disease, we investigated metallothionein (MT) levels in ALS organs and serum. We previously reported significantly increased MT levels in ALS liver and kidney. These are not reflected in serum MT levels, which are normal in ALS. In ALS spinal cord, MT is expressed in gray matter protoplasmic astrocytes. Induction of MT synthesis in ALS may denote increased metal exposure or may result from increased oxidative stress, as in familial ALS.