AbstractHexagonal crystals of turkey egg white lysozyme have been examined for activity in order to evaluate their potential for use in time‐resolved X‐ray crystallographic experiments. Substrates used in this study were hexa‐N‐acetylglucosamine (hexa‐GlcNAc) and a modified analogue of hexa‐GlcNAc where the terminal sugar ring was opened by reduction with tritiated sodium borohydride. This gave a labeled β‐N‐acetylglucosaminitol unit at the sixth position of the sugar chain and allowed easy quantitation of enzymatic cleavage on TLC plates. Using these substrates, it has been shown that turkey egg white lysozyme is enzymatically active in the crystal. Enzyme dispersed in the buffer surrounding the crystal does not show detectable activity under conditions relevant to an X‐ray experiment. Unmodified hexa‐GlcNAc is hydrolyzed into di‐, tri‐, and tetrasaccharides in the crystal. This cleavage pattern is different from that obtained with hen egg white lysozyme in solution and likely causes of the differences are discussed. The reduced radiolabeled oligosaccharide has a unique cleavage pattern with trisaccharides as the products. The specific activity of the enzyme with the radiolabelled analogue was 9.8 (± 1.0) × 10−7mmol/min/mg pr