The molecular and biochemical characterization of many components of the phagocyte oxidase complex that generates superoxide have greatly advanced our understanding of this important pathway. Genetic defects in one or more of the components of this host defense system result in the chronic granulomatous disease phenotype. Biochemical advances and the results of a clinical trial that established the efficacy of recombinant human interferon-gamma for prophylaxis of infections in chronic granulomatous disease are the highlights of recent achievements in this area of phagocyte biology.