The complete catalytic hydrogenation of the 4, 5-double bond of pyrimidine nucleotides has been carried out under mild conditions with a rhodium catalyst. Dihydrouridylic acid, formed from either uridylic or cytidylic acid, is cleaved by dilute alkali at room temperature to give the N-ribosyl phosphate of 0-ureidopropionic acid. Dilute acid at room temperature hydrolyzes this substance to ribose phosphate and P-ureidopropionic acid without appreciable ...