PURPOSE OF REVIEW: During the past 2 years a number of studies, meta-analyses and reviews have shown that micronutrient supplementation may be beneficial in critical illness. Selenium is emerging as a particularly important micronutrient. This paper reviews the evidence from trials in the critically ill, putting mechanisms, methods and shortcomings into perspective. RECENT FINDINGS: There is growing evidence that antioxidant supplements, particularly high-dose selenium, may reduce mortality, infectious complications, and improve wound healing. Deleterious effects may result from prolonged high doses, whereas short-term high dose supplements are probably safe in most critically ill populations. SUMMARY: Plasma micronutrient concentrations are low during critical illness, as a result of losses, low intakes and dilution, and redistribution from plasma to tissues. An assessment of status is difficult. Micronutrient supplements appear beneficial in conditions such as major burns, trauma and sepsis and stroke, and are most likely to benefit patients with previous or actual depletion. The intravenous route seems more efficient than the enteral. Although chronic high intakes may be harmful, short-term interventions appear to be free of deleterious effects. Further research is required to determine the optimal micronutrient combinations and the doses required according to the timing of intervention and severity of disease.