Nucleoside diphosphate kinase (NDK) catalyses the transfer of the gamma-phosphoryl group from a nucleoside triphosphate (NTP) to a nucleoside diphosphate (NDP). NDK is involved in and required for coleoptile elongation in rice. The level of the enzyme changes during seed germination and the early stages of seedling growth. Recombinant rice NDK (rNDK) has been crystallized using the hanging-drop vapour-diffusion method. rNDK crystals diffracted to a resolution of 2.50 Angstrom and belong to space group P2(1)2(1)2(1), with unit-cell parameters a = 70.98, b = 182.26, c = 188.30 Angstrom. Preliminary analysis indicates there to be 12 rNDK molecules in each asymmetric unit, with a solvent content of 47.2%.