Four groups of six volunteers were given continuous infusions of glucose, fructose, sorbitol and xylitol in a dosage of 0.25 g/kg body weight over 48 hours. All solutions were well tolerated provided that potassium was supplemented in sufficient amounts. During the first 12 hour period of xylitol infusion renal potassium loss was greater than during infusion of all other substrates. No substantial differences in the alterations of the other parameters were noted between glucose and glucose substitutes. The only exception was the rise in serum uric acid concentration during infusion of xylitol and of fructose, which was not noted during infusion of glucose or sorbitol. The concentration of serum bilirubin was elevated during infusion of all four substances. The decrease in serum free fatty acid concentration was equally caused by glucose, fructose, xylitol or sorbitol. The increase in serum triglyceride concentration was observed earlier during the infusion of glucose substitutes as compared to glucose. Blood glucose concentration was only elevated during infusion of glucose. In the post infusion period there was quick rise in fatty acid concentration after cessation of glucose infusion. This normalisation occurred more slowly after stopping fructose and particulary xylitol or sorbitol. These results have no indications for adverse effects of the continuous infusions of glucose or glucose substitutes.