There have been recent reports of hospitalised patients developing clinical thiamine deficiency, combined with much debate on the optimal supplementation of thiamine for the parenterally fed patient, particularly in the intensive therapy environment. We performed a retrospective study on 158 patients admitted to the Intensive Care Unit who required nutritional support. Patients who survived had significantly higher body thiamine status than those who died (p less than 0.01). There was no difference between serum albumin concentrations of the two groups. Twenty percent of the patients had biochemical evidence of thiamine deficiency and the mortality rate in these patients was 72% as compared with 50% mortality overall. Follow-up results suggest that current levels of thiamine supplementation are insufficient for critically ill intravenously fed patients. We suggest that patients be given a loading dose of 50-250 mg thiamine on admission to the Intensive Care Unit.