Abstract The influence of tolbutamide on the glycogen content of the liver, the blood-sugar level, and the absorption of carbohydrates, has been studied. Tolbutamide, 100 mg/kg body weight, reduces the blood-sugar level, after oral administration of glucose, fructose or galactose, to a level below that of the controls. With tolbutamide and fructose there is a significant decrease in the amount of glycogen in the liver after 2 1 2 hours as compared to the fructose controls. This effect was less pronounced in analogous experiments with glucose or galactose. It follows that the hypoglycaemic effect of tolbutamide does not result from an increase of the glycogen content of the liver. In one experiment an inhibitory action of tolbutamide on the absorption of fructose was shown. No influence on the absorption of glucose or galactose was observed. Tolbutamide, 250 mg/kg body weight, administered without carbohydrates causes an increase in the amount of glycogen of the liver after 7 hours ; the blood-sugar level decreases.