Nonproductive and productive interactions of lysozyme with some β-aryl di-N-acetylchitobiosides were studied. Difference ultraviolet and proton magnetic resonance spectroscopic methods were used to examine the nature and extent of nonproductive interactions. In the nonproductive binding mode, two glycose residues interact with subsites B and C. Information concerning productive interactions was deduced indirectly from rates of phenol liberation and from product analyses. The productive binding modes which place two glycose residues either at subsites C and D, or at subsites D and E, are consistent with experimental results. The contribution of the aryl aglycone to nonproductive and productive interactions suggests that there is flexibility of substrate specificity in lysozyme catalysis.