Dysfunction of NADPH oxidase results in chronic granulomatous disease (CGD), a syndrome characterized by severe bacterial and fungal infections. Phagocytes of the patients are unable to kill ingested microorganisms which leads to the formation of granulomas and abscesses. Predominant pathogens are the catalase-positive bacteriae (Staphylococcus aureus) and some fungi (Aspergillus species). Infections of these patients should be treated by antimicrobial agents, which penetrate cells and kill pathogens inside. The aim of this study was to give a short description of the structure and function of the NADPH oxidase enzyme and to summarize the results obtained during the diagnostic of 10 patients with chronic granulomatous disease. Characterization of the disease was confirmed by mutation analyses.