X-ray diffraction data were collected at the IMCA-CAT 17-ID beamline of Advanced Photon Source at Argonne National Labs and processed using autoPROC. Structure of the SARS CoV main protease in complex with PF-835231 was determined by molecular replacement using the published protein structure (PDBID 1Q2W) as the starting model in program Phaser and refined iteratively using autoBUSTER followed by model building in Coot.