Total parenteral nutrition is one of the most important recent advances in medicine. The delivery of total parenteral nutrition, however, can be associated with a broad spectrum of complications ranging from mechanical (catheter related) to metabolic. We have recently seen a previously unreported complication of total parenteral nutrition - three patients maintained on total parenteral nutrition, who did not receive vitamins and experienced the acute onset of life-threatening metabolic acidosis with pH values as low as 6.70. All responded promptly and completely to the administration of intravenous thiamine, and thus were probably examples of acute beriberi. Acute beriberi is a well-documented syndrome which usually occurs in nutritionally compromised individuals outside the hospital setting who lack thiamine in their diet. Without thiamine, glucose cannot enter the Krebs cycle in order to be completely oxidized for energy production and therefore, accumulates as lactic acid. This lactic acidosis is refractory to any treatment except thiamine and will result in cardiovascular collapse if the vitamin is not administered.