We clearly observed the dislocation of protein crystals by means of synchrotron white-beam topography. According to the invisibility criterion (g . b = 0) of dislocation images, it was found that the predominant dislocations are of screw character with Burgers vector b = (110). These results are discussed in terms of elastic energy of dislocations. (C) 2007 Published by Elsevier B.V.