The spontaneous reduction of nitroblue tetrazolium (NBT) was found to be significantly elevated in phagocytes of normal newborn in fants in the absence of infection. This was evident using both a simple histochemical test and a more elalborate quantitative test for NBT reduction. During phagocytosis of latex particles, the expected rise in NBT reduction was significantly greater in neonatal phagocytes than in phagocytes of control subjects. The increased NBT reducing activity of neonatal neutrophils makes it impossible to use the NBT histochemical test for tile detection of bacterial infection in that age group. However, NBT-reduction tests can be used with profit in the neonatal period to diagnose chronic granulomatous disease when a positive family history warrants such an investigation. [See pdf for the Figure]