Specific ATP-phosphotransferases for glucose, fructose and mannose, and glucosephosphate and mannosephosphate isomerases have been extracted from Chaetomium globosum. The fructokinase is stabilized by potassium whereas the glucokinase is activated by this cation, but is, otherwise, more stable than the former. The less-studied mannokinase showed no requirement for potassium. The inhibition of the fructokinase by glucose and mannose, and of the glucokinase by mannose are detailed, together with pH optima, Km values and other properties of the enzymes. The level of glucosephosphate isomerase was found to be higher in fructose-grown than in glucose-grown mycelium. The role of the enzyme systems in the absorption and utilization of exogenous hexoses is discussed.