Dihydropyrimidinases are involved in the reductive pathway of pyrimidine degradation, catalysing the hydrolysis of 5,6-dihydrouracil and 5,6-dihydrothymine to the corresponding N-carbamoyl beta-amino acids. This enzyme has often been referred to as hydantoinase owing to its industrial application in the production of optically pure amino acids starting from racemic mixtures of 5-monosubstituted hydantoins. Recombinant dihydropyrimidinase from Sinorhizobium meliloti CECT4114 (SmelDhp) has been expressed, purified and crystallized. Crystallization was performed using the counter-diffusion method with capillaries of 0.3 mm inner diameter. Crystals of SmelDhp suitable for data collection and structure determination were grown in the presence of agarose at 0.1%(w/v) in order to ensure mass transport controlled by diffusion. X-ray data were collected to a resolution of 1.85 A. The crystal belongs to the orthorhombic space group C222(1), with unit-cell parameters a = 124.89, b = 126.28, c = 196.10 A and two molecules in the asymmetric unit. A molecular-replacement solution has been determined and refinement is in progress.