To investigate the role of metallic elements in motor neuron disease (MND), we used a photon-excited, energy-dispersive x-ray analytical system to measure the metal content of muscle biopsies from 21 patients with MND and compared the results with those obtained from biopsies from neurologically diseased control patients matched for age, sex, and muscle biopsied. By t test analysis, the MND patients did not differ significantly from controls in the average muscle biopsy concentrations of lead, mercury, arsenic, manganese, aluminum, or any of the other ten elements measured. Subgroup analysis showed that women with MND had less barium (p < 0.05) and iron (p < 0.01) in their muscles than controls, a finding probably an artifact of the multiple statistical analyses done on the data. Metallic content of muscle, for unknown reasons, tends to decrease with age in MND, but increases with age in controls. The evidence indicates that the muscle content of heavy metals in patients with MND does not differ from that in matched controls and that in MND, muscle does not store toxic metals for retrograde transport to anterior horn cells, as has been postulated by others.