Glucose, fructose and galactose have been administered intravenously over several hours to healthy persons; different administration rates were used. These sugars were measured enzymatically in serum and urine. Moreover, insulin (IMI) and uric acid were also determined (the latter for fructose only). Glucose and fructose are equally well utilized, galactose is unsuited for parenteral feeding due to caloric restriction and toxic side-effects. High-fructose loads (1.5 g/kg body weight/h) were followed by a significant rise of serum uric acid, lower infusion rates did not show alterations of uric acid, however. All hexoses are followed by an elevation of plasma insulin, although the increase during galactose and fructose infusions is only moderate in comparison with glucose. Finally, the above-mentioned results are compared with xylitol, a pentose frequently used for parenteral nutrition.