In this study, we investigated the possibility of using a modified hydantoinase process for the production of optically pure beta-amino acids. Two aryl-substituted dihydropyrimidines -6-phenyl-5,6-dihydrouracil (PheDU) and -chloro--6-phenyl-5,6-dihydrouracil (ClPheDU) were synthesized. Hydrolysis of these novel substrates to the corresponding -carbamoyl-beta-amino acids by three recombinant -hydantoinases and several bacterial strains was tested. All applied recombinant -hydantoinases and eight bacterial isolates catalyzed the conversion of PheDU to -carbamoyl-beta-phenylalanine (C beta Phe). Some of these biocatalysts showed an enantioselectivity for either the - or the -PheDU enantiomer. The second dihydropyrimidinase substrate ClPheDU was hydrolyzed by all three recombinant -hydantoinases and six of the wild-type strains. To our knowledge, this is the first dihydropyrimidinase activity reported with this aryl-substituted dihydropyrimidine. For selected biocatalysts, hydantoinase activity towards aryl-substituted hydantoins was demonstrated as well. However, none of the bacterial strains tested so far exhibited any carbamoylase activity towards C beta Phe.