Deficiencies of selenium (Se) and vitamin E can result in myopathies in cattle and sheep but the mechanics have not been clearly described. Both Se, as a component of the enzyme glutathione peroxidase, and vitamin E as a radicle scavenger, are involved in the protection of cells against the toxic effects of oxygen. In young calves, Se/vitamin E deficiency can result in the death of the animals due to a focal myopathy occurring in heart muscle; focal lesions are also found in skeletal muscle. In older calves, a more diffuse myopathy is usually confined to skeletal muscle and usually occurs when cattle are turned out from winter housing to spring pasture. However, low Se/vitamin E status will not invariably result in clinical symptoms of myopathy and other factors may be involved. This report describes some of the biochemical changes which can occur during the onset of clinical myopathy in Se/vitamin E-deficient cattle.