THE enzyme glucose-6-phosphatase cannot be classified as either acid phosphatase or alkaline phosphatase. It is highly specific and is differentiated from non-specific acid and alkaline phosphatases on the basis of location and behaviour. So far, no systematic study has been made regarding the distribution of this enzyme in different species of animals. Hers and de Duve1 first reported that in rats it is abundant in the liver, but only present in small amounts in the kidney; it is, however, absent in the intestine and not present in detectable amount in other organs and blood. But afterwards they contradicted their own previous finding and showed that glucose-6-phosphatase was also present in the intestine. The present communication concerns an investigation of the distribution of this enzyme in different species of animals. © 1963 Nature Publishing Group.