Plasma chitotriosidase originates from activated macrophages and is reported to be elevated in many Lysosomal Storage Disorders. Measurement of this enzyme activity has been an available tool for monitoring therapy of Gaucher disease. The degree of elevation of chitotriosidase is useful for differential diagnosis of Gaucher disease and Niemann Pick A/B. However the potential utility of this chitotriosidase assay depends on the frequency of deficient chitotriosidase activity in a particular population. We therefore aim to study the clinical utility of this assay Gaucher and Niemann Pick A/B diseases in the backdrop of chitotriosidase deficiency in our population. The study comprises 173 patients with clinical suspicion of either Gaucher disease (n=108) or Niemann Pick A/B (n=65) and 92 healthy controls. The plasma samples of controls, Gaucher disease, and Niemann Pick A/B showed chitotriosidase deficiency of 12%, 25% and 27% respectively. The degree of elevation of chitotriosidase in Gaucher disease and Niemann Pick A/B patients is 40-326 (11,325.7±6395.4nmol/h/ml) and 7-22 folds (1192.5±463.0nmol/h/ml) respectively. In view of these findings of distinguishable fold elevation of chitotriosidase in Gaucher disease or Niemann Pick A/B, it can be a potential surrogate differential diagnostic marker for these groups of diseases, except in the patients in whom this enzyme is deficient.