Thermus thermophilus is an aerobic chemoorganotroph that has been found to grow anaerobically in the presence of nitrate. Crystals of glucose dehydrogenase (GDH) from T. thermophilus HB8 belong to space group P2(1), with unit-cell parameters a = 36.90, b = 132.96, c = 60.78 A, beta = 97.2 degrees. Preliminary studies and molecular-replacement calculations reveal that the asymmetric unit contains two monomers.