The extracellular domain (residues 1 to 220) of human tissue factor has been cloned and expressed in Escherichia coli and purified to isoelectric homogeneity. Single crystals suitable for X-ray analysis have been obtained by vapour diffusion. They belong to the tetragonal space group P4(1)2(1)2 or P4(3)2(1)2 with a = b = 45.2 A, c = 231.5 A, contain one molecule per asymmetric unit and diffract to 2.6 A resolution. Native and derivative data sets have been collected to 3.6 and 3.9 A, respectively.