The rocking curve widths of tetragonal lysozyme crystals were treasured. Typical full-width half-maximum (FWHM) of the rocking curve of crystals grown from a pure lysozyme solution were 0.004-0.006 degrees, while those crystals containing 5% lysozyrne dieter were 0.006-0.010 degrees. X-ray topography experiments revealed that dislocations existed in crystals containing the lysozyme dieter. These dislocations are one of the causes of rocking curve width broadening. 2 x 10(4) cm(-2) pits were observed on the {1 0 1} face in contaminated crystals, but few, if any pits were observed in either face of the pure crystals. (c) 2006 Elsevier B.V. All rights reserved.