AbstractUridine diphosphate-N-acetylglucosamine: lysosomal enzyme precursor N-acetyl-glucosamine-1-phosphate transferase, is a key enzyme involved in the intracellular targeting of lysosomal enzymes. This enzyme is elevated fourfold in primary ovarian tumor microsomes with respect to normal ovarian microsomes. This elevation is associated with significant increases in the specific activity of multiple lysosomal hydrolases, includingβ-D-hexasaminidase,α-L-fucosidase, andβ-D-galactosidase. The activity of the phosphotransferase was also documented in several cell lines derived from human tumors. The possible role of this enzyme in tumor-associated phosphorylation is discussed.