Neutrophils play a crucial role in the innate immune system by phagocytosing, killing, and digesting bacteria and fungi. Initially, it was believed that this process was primarily driven by oxygen free radicals and reactive oxygen species (ROS) produced by the NADPH oxidase, as well as oxidized halides from myeloperoxidase. However, recent studies have shown that these mechanisms are not sufficient for effective microbial killing. Instead, the NADPH oxidase generates superoxide, which pumps electrons into the phagocytic vacuole, creating a charge that must be compensated. This compensation involves the movement of ions, primarily potassium (K+) and chloride (Cl-), which alter the conditions within the vacuole, making it more conducive to microbial killing and digestion by enzymes released from cytoplasmic granules. The granules contain a variety of antimicrobial proteins, including neutrophil elastase (NE), cathepsin G, and defensins, which are activated by the hypertonicity and alkalinity induced by the NADPH oxidase. The combination of NADPH oxidase activity and neutral proteases is essential for effective microbial killing. The review also discusses the limitations in understanding the killing systems, the molecular genetics of chronic granulomatous disease (CGD), and the role of myeloperoxidase-mediated halogenation. Finally, it highlights the importance of the granule contents in the killing process and the need to resolve several unresolved questions about charge compensation across the vacuolar membrane.Neutrophils play a crucial role in the innate immune system by phagocytosing, killing, and digesting bacteria and fungi. Initially, it was believed that this process was primarily driven by oxygen free radicals and reactive oxygen species (ROS) produced by the NADPH oxidase, as well as oxidized halides from myeloperoxidase. However, recent studies have shown that these mechanisms are not sufficient for effective microbial killing. Instead, the NADPH oxidase generates superoxide, which pumps electrons into the phagocytic vacuole, creating a charge that must be compensated. This compensation involves the movement of ions, primarily potassium (K+) and chloride (Cl-), which alter the conditions within the vacuole, making it more conducive to microbial killing and digestion by enzymes released from cytoplasmic granules. The granules contain a variety of antimicrobial proteins, including neutrophil elastase (NE), cathepsin G, and defensins, which are activated by the hypertonicity and alkalinity induced by the NADPH oxidase. The combination of NADPH oxidase activity and neutral proteases is essential for effective microbial killing. The review also discusses the limitations in understanding the killing systems, the molecular genetics of chronic granulomatous disease (CGD), and the role of myeloperoxidase-mediated halogenation. Finally, it highlights the importance of the granule contents in the killing process and the need to resolve several unresolved questions about charge compensation across the vacuolar membrane.