Objective: This study is undertaken to study the efficacy of Nitroblue tetrazolium test (NBT), which is a simple test to evaluate neutrophilic functions in bacterial and non-bacterial infectious diseases. Study design: This is a prospective study from June 2012 to December 2013 at a tertiary care centre. Materials And Methods: This study included 120 cases of febrile illnesses, with age varied from 18 months to 23 years (mean age and median age 12.3years), with equal sex distribution of 1:1. Results: In normal healthy controls the NBT positive ranges for unstimulated are 6.5% (2-11) and stimulated are 64.5% (48-81) respectively. The cases of septicemias, broncho pneumonia, pharyngitis, pyogenic meningitis, pyodermas and pyrexia of unknown origin etc have registered a high unstimulated NBT positively and stimulated NBT positive cells. 66% (45-85) the cases of immuno deficiency diseases registered very low NBT positively in both unstimulated 2.5% (1-4) and stimulated 3% (1-5) respectively. Conclusion: The NBT test is proved to be useful as a simple diagnostic aid in differentiating patients with bacterial infections from individual with non bacterial diseases. The proportion of absolute number of NBT positive neutrophils serve as a measure of the adequacy of the host response to infection.