Human coagulation factor VIIai that lacks the Gla domain (residues 1-44) has been prepared, purified, and crystallised, First, recombinant factor VII was activated to form factor VIIa, the active site was then inhibited with 1,5-dansyl-Glu-Gly-Arg-chloromethyl ketone, and finally the Gla domain was removed by chymotryptic digestion, yielding factor VIIai (des-Gla). After further purification single crystals suitable for x-ray analysis were obtained by vapour diffusion. Crystals of factor VIIai (des-Gla) belong to the tetragonal space group P4(1)2(1)2 or P4(3)2(1)2 with unit cell dimensions a = b = 94.85 Angstrom, c = 114.30 Angstrom contain one molecule per asymmetric unit, and diffract to 2.3-Angstrom resolution when exposed to synchrotron radiation.