Several of the antioxidant enzymes are metalloenzymes, which contain trace minerals for which vegetables and fruit are significant sources. Mitochondrial superoxide dismutase is a manganese-containing enzyme. Glutathione peroxidases are selenium-dependent enzymes. Vegetables and fruit are rich sources of manganese, are but not typically significant sources of selenium. However, selenium is found in plant tissues in amounts proportional to the mineral concentration of the soil in which the plant grows (2). Thus, depending on the location, vegetables and fruit can be sources of selenium for some populations. Certain patients (eg, organ transplant patients and those receiving chronic hemodialysis) tend to be selenium deficient and to have compromised antioxidant systems as a result of their diseases and treatments (7, 8). Results of studies conducted in these patients show that selenium supplementation improves the oxygen radical scavenger system, decreases the susceptibility of plasma lipids to peroxidation, lowers oxidized glutathione content of erythrocytes, and increases erythrocyte selenium-dependent glutathione peroxidase activity (7, 8).