Crystals of the diphtheria tox repressor (DtxR) from Corynebacterium diphtheriae suitable for structure determination have been obtained. DtxR activated with transition metal ions represses the expression of the structural gene for the diphtheria toxin, tox, which is encoded on the genome of a family of closely related corynebacteriophages. The space group of the obtained crystals is trigonal P3(1)21 or its enantiomorph P3(2)21 with a = b = 64.2 A, c = 220.5 A, alpha = beta = 90 degrees, gamma = 120 degrees. Two monomers comprise the asymmetric unit. The crystals diffract to a resolution of better than 3 A.