Abstract The ketokinase activity of homogenates of intestinal mucosa has been found to involve two enzymes, a heat-stable ketokinase which has a high affinity for fructose and sorbose and a heat-labile ketokinase which shows low affinity for both ketoses. The ketoses appear to be phosphorylated by both enzymes in the 1 position. The heat-stable ketokinase has properties similar to the liver ketokinase and its presence in the intestinal mucosa is compatible with the hypothesis that the mechanism of the transformation of fructose into glucose that takes place in the intestinal mucosa might be essentially the same that operates in liver.