The aim of this study was to determine the role of reactive oxygen species (ROS) in checking the growth of intracellular mycobacteria within human phagocytes. Peripheral blood-derived neutrophils and monocyte-derived macrophages were isolated from Chronic Granulomatous Disease (CGD) patients and normal healthy human volunteers. CGD patients are known to have a defect in the NADPH oxidase pathway, resulting in their neutrophils and monocyte-derived macrophages being unable to generate oxygen radicals which are required to kill intracellular bacteria. The cells were then infected with Bacille Calmette Guerin (BCG) or Mycobacterium avium, and the bacterial growth in each cell type determined by Colony Forming Units (CFU) estimate. The results obtained indicate that there was no demonstrable inhibition in the intracellular mycobacterial growth within neutrophils or macrophages derived from either Chronic Granulomatous Disease (CGD:deficient in NADPH oxidase pathway) or normal healthy volunteers. Macrophage treatment with either IFN-gamma or TNF-alpha had no effect.