Autolysis of isolated cell walls of Staphylococcus aureus strain Copenhagen was accompanied by the release of 1 mole of N-terminal alanine per mole of glutamic acid. No other N-terminal amino acids and no C-terminal amino acids were released. These observations indicated that complete hydrolysis of N-acetylmuramyl-l-alanine linkages ("amidase" action) had occurred. This was confirmed by fractionation and analysis of the products. Hydrolysis of 4-O-beta-N-acetylglucosaminyl-N-acetylmuramic acid linkages also occurred to a variable extent; on one occasion, complete degradation to disaccharides and hexosamine-free polypeptides (with intact pentaglycine cross-bridges) occurred. In one other instance, hydrolysis within pentaglycine bridges also occurred. Analyses of intact cell walls indicated that, in vivo, glycine endopeptidase activity was negligible and amidase activity was low, but that endo-beta-N-acetylglucosaminidase hydrolysed about 8% of the N-acetylglucosaminyl-N-acetylmuramic acid linkages. Autolysis of isolated cell walls was too slow for the enzymes isolated with them to have significant action during this isolation. The possible functions of these autolytic activities are discussed.