Most frequent types of microcytic anaemia in Indian patients are Iron Deficiency Anaemia (IDA) and Beta Thalassemia Trait (BTT).We retrospectively judged the reliability of Mentzer index for differential diagnosis of microcytosis Methods. A total of 33 randomly selected patients with different age group were evaluated. We calculated 6 discrimination RBC indices in all with consideration of RBC histogram. All the samples were also tested for HbA2,serum iron, TIBC and Iron saturation. Results:   Mentzer index showed GOOD sensitivity.