The purine repressor (PurR) is a DNA-binding protein, which together with a purine corepressor serves to regulate de novo purine and pyrimidine biosynthesis in Escherichia coli. PurR belongs to the structurally homologous lac repressor family of transcription regulators. A PurR-hypoxanthine-DNA complex has been crystallized, with DNA encompassing the high affinity purF operator site and which is 16 base-pairs long with 5'-deoxynucleoside overhangs on each complementary strand. The crystals diffract to better than 2.6 A and take the orthorhombic space group C222(1), with unit cell dimensions a = 175.9 A, b = 94.8 A and c = 81.8 A. The structure determination of this PurR-hypoxanthine-DNA complex will provide the first high resolution view of a Lacl member-DNA complex.