Modification of cell surface molecules with sialic acid is crucial for their function in many biological processes, including cell adhesion and signal transduction, Uridine diphosphate-N-acetylglucosamine 2-epimerase (UDP-GLcNAc 2-epimerase) is an enzyme that catalyzes an early, rate-limiting step in the sialic acid biosynthetic pathway. UDP-GlcNAc 2-epimerase was found to be a major determinant of cell surface sialylation in human hematopoietic cell Lines and a critical regulator of the function of specific cell surface adhesion molecules.