Uridine-d2 is intended for use as an internal standard for the quantification of uridine by GC- or LC-MS. Uridine is a pyrimidine nucleoside composed of uracil and ribose. It forms complementary base pairs with adenosine in RNA. Uridine can be catabolized to uracil via uridine phosphorylase, and it can be phosphorylated to uridine-5’-monophosphate by uridine-cytidine kinase (UCK). It is replaced with thymidine in DNA.