Abstract 1. 1. 2-Acylamido derivatives of 2-deoxy- d -glucose have been tested as inhibitors of the lysis of Microccocus lysodeikticus cell suspensions by lysozyme (mucopeptide N -acetylmuramylhydrolase, EC 3.2.1.17) at pH 6.2. 2. 2. Only the 2-acetamido derivative was found to be effective as an inhibitor amongst the reducing derivatives and at lower concentrations the β anomer was approx. 10 times more inhibitory as the α anomer. 3. 3. The methyl 2-acetamido-2-deoxy- d -glucosides were found to be equally effective inhibitors as the corresponding reducing derivatives, at lower concentrations the same difference being found between the α and β anomers. The results obtained from testing the β anomer over a wide concentration range suggest that two binding sites for inhibition exist in the lysozyme molecule. The ethyl 2-acetamido-2-deoxy- d -glucosides only showed inhibition at relatively high concentrations. 4. 4. The difference spectra of lysozyme in the presence of the derivatives tested showed a rough correlation with the inhibitory power of the derivatives. All spectra obtained displayed a profile typical of indole perturbation. 5. 5. The inhibitory power of some derivatives was tested at pH 9.2 and was found to be more effective at this pH. 6. 6. With the aid of the crystallographic model of lysozyme an attempt has been made to correlate the structure and anomeric configuration of the derivatives tested with the steric requirements of the postulated binding sites.