The osmotic fragility test is used to determine the extent of red blood cell haemolysis produced by osmotic stress. Since the quality of this test may easily be influenced by environmental and technical factors we have determined osmotic fragility reference values in our own conditions. The results show significantly increased osmotic resistance of erythrocytes in our conditions vs the published values for blood samples anticoagulated with heparin. Furthermore, the use of EDTA as an anticoagulant increased the osmotic fragility of red blood cells as compared with heparin. We conclude that EDTA can be used as an anticoagulant for the osmotic fragility test in order to simplify routine procedures. However, every laboratory should determine its own reference values which would reflect the local environmental and technical factors.