Five biochemically severe cases of thiamine deficiency presented to one medical firm within an 11-month period at a district general hospital in Wales. In two patients the presenting feature was oliguric functional renal failure, with frank cardiovascular beri-beri. In one of these renal failure developed over a period of seven days, the cause being recognised after 20 days of continuous high-calorie intravenous feeding including daily vitamin supplements. Three further cases illustrate how early recognition and adequate treatment of the renal and cardiovascular components of thiamine deficiency may be life-saving.