Complete blood count (CBC) parameters of 2196 certainly diagnosed (1272 beta-thalassaemia minor and 924 iron deficiency) samples were used to evaluate the following indices and formulas: Bessman index (RDW), Mentzer formula (MCV/RBC), England and Fraser formula (MCV - RBC - 5 x Hb- 3.4), Shine and Lal formula (MCV2 x MCH/100), Ehsani formula (MCV-10 x RBC), Srivastava formula (MCH/RBC), Green and King formula (MCV2 x RDW/Hb x 100), red distribution width index RDWI (RDW x MCV/RBC), RDW/RBC, as well as our formula (MCV-RBC -3 x Hb).