Erythrocytes affected by age and diseases such as sickle cell anemia, hypertension, diabetes, etc.. exhibit abnormally high intracellular Ca2+ ion levels, and appear to have altered cytoskeleton properties. It has been proposed that extra binding of Ca2+ to inernbrane-associated calmodulin attenuates the spectrin-ankyrin-Band 3 tether of the cytoskeleton to the cytoplasmic membrane and might change the cytoskeleton structure. Due to the close apposition of the network, direct observation Of Such a structural change in vivo is restricted. In this study, atomic force microscopy and quantitative image analysis were applied to investigate the structural change of young healthy erythrocyte cytoskeletons upon extra Ca2+ binding to the cytoplasmic membrane in vitro. The results show that extra Ca2+ binding increased the cytoskeletons rigidity and prevented spectrin aggregation during sample preparation. The cytoskeleton morphology observed in Ca2+-incubated healthy young cell were similar to the glutaraldehyde-fixed healthy young cells. © 2005 Elsevier Inc. All rights reserved.