The genes encoding the tRNA-modifying enzyme S-adenosylmethionine:tRNA ribosyl transferase/isomerase (QueA) from 12 eubacterial sources were overexpressed in Escherichia coli and the resulting products were purified to homogeneity and subjected to crystallization trials. Using the hanging-drop vapour-diffusion method, crystals suitable for X-ray diffraction experiments were only obtained for the queA gene product from Bacillus subtilis. The crystals belong to the space group P422, with unit-cell parameters a = b = 100.7, c = 150.9 A. Using highly focused synchrotron radiation from the EMBL/ESRF beamline ID13 (Grenoble, France), diffraction to at least 3.2 A could be achieved. A selenomethionyl derivative of the protein was prepared and crystallized for future multiwavelength anomalous diffraction (MAD) experiments.