Dihydrouracil is an intermediate in the catabolism of uracil. The enzyme dihydrouracil dehydrogenase (NAD+) converts uracil to dihydrouracil:
The enzyme uses reduced nicotinamide adenine dinucleotide (NADH) as its cofactor.
Dihydrouracil is the base present in the nucleoside dihydrouridine.