Dihydroorotase (EC 3.5.2.3, carbamoylaspartic dehydrase, dihydroorotate hydrolase) is an enzyme which converts carbamoyl aspartic acid into 4,5-dihydroorotic acid in the biosynthesis of pyrimidines. It forms a multifunctional enzyme with carbamoyl phosphate synthetase and aspartate transcarbamoylase. Dihydroorotase is a zinc metalloenzyme.