The release of reactive oxygen species is an important factor in the development of sepsis induced multiorgan dysfunction syndrome. Common protection mechanisms are impaired in this syndrome. Serum levels of selenium, a cofactor of the glutathionperoxidase, are reduced. Several studies suggest a benefit of selenium application in patients with severe sepsis but data from large clinical trials are not available. After inclusion into the study, patients are randomly allocated to a placebo or selenium group. Treating physicians and patients are blinded regarding the allocation. The selenium group receives sodium selenite intravenously - 1000 µg as a bolus followed by a continuous infusion of 1000 µg per day until the end of ICU treatment but not longer than 21 days.