Detergent-solubilized human liver glucose-6-phosphatase (d-glucose-6-phosphate phosphohydrolase, EC 3.1.3.9) has been found to have inorganic phyrophosphatase (pyrophosphate phosphohydrolase, EC 3.6.1.1) and pyrophosphate-glucose phosphotransferase activity (not yet classified). It is composed primarily of lipid and protein, with a small amount of RNA, and trace amounts of calcium and magnesium. Pigs and rabbits were immunized with it, and the antiserum also reacted with similar preparations from human kidney and intestine, and also from monkey and guinea pig liver. Liver from a child with glycogen storage disease, type I, did not produce a precipitin line in agar when it was diffused into the antiserum. © 1968.