The polymorphonuclear leukocyte (neutrophil) is the most important phagocytic cell that defends the host against acute bacterial infection. Disorders of neutrophil function are suggested by recurrent cutaneous, periodontal, respiratory, or soft tissue infections. Staphylococcus aureus, gram-negative bacilli, and less commonly, Candida albicans, are the causative organisms. Treatment is supportive involving surgical drainage and antibiotics. Bone marrow transplantation offers hope to some patients. The biochemical and molecular defects have been identified for some of these disorders. Identification of these defects and their physiologic consequences have improved our understanding of how the activated neutrophil is attracted and adheres to inflammatory sites, and produces toxic products that destroy bacteria. However, the activated neutrophil may also damage normal tissue and participate in diseases such as rheumatoid arthritis and the adult respiratory distress syndrome (ARDS).