Crystal defects, especially dislocations, in hen egg-white lysozyme crystals that have multiple polymorphisms, for example, tetragonal, orthorhombic, monoclinic forms, etc., were investigated by means of synchrotron monochromatic-beam X-ray topography. The observed topographic images of dislocations were much clearer compared to those of any protein crystals that have been reported so far. It was demonstrated that millimeter-size crystals larger than extinction lengths for X-ray topographic reflections are required to obtain clear images, that is, direct images, for protein crystals. In addition, the weak-beam technique was found to be useful for obtaining clearer images. Straight, curved, and loop-type dislocations were clearly resolved on the topographs. This shows that dislocations observed in common inorganic crystals and organic crystals of small molecules can also be introduced even into protein crystals. The shape and configuration of dislocations strongly depended on the crystal form. This suggests that the growth mechanisms in the different crystal forms studied may differ. X-ray topography provides a useful tool for the characterization of protein crystal dislocations.

Dislocations in large hen egg‐white lysozyme (HEWL) crystals with tetragonal and orthorhombic forms were investigated by means of synchrotron monochromatic‐beam X‐ray topography. For the tetragonal form, not only screw dislocations but also edge ones are found to be included in predominant ones parallel to 〈110〉 directions. In addition, curved dislocations that can be related to (001)〈110〉 slip system are observed at the crystal edges. For the orthorhombic form, predominant edge dislocations with [001] Burgers vector are stereoscopically observed. It is clarified that they are generated at or around the nucleus centre or sector boundary.