Treatment of Staphylococcus aureus in vitro with cationic agents results in the activation of their autolytic wall enzymes and in the degradation of their cell walls. Exposure of staphylococci either to hydrogen peroxide or the proteinases abolished the autolytic process. This effect was totally reversed by catalase and by proteinase inhibitors, respectively. It is suggested that the failure of neutrophils and macrophages to effectively degrade microbial cell wall components in inflammatory sites might be due to the inactivation of the autolytic wall enzymes of bacteria by hydrogen peroxide and by proteinases generated by the activated leukocytes. This might explain the prolonged chronic inflammatory sequelae seen following infections.