SIALIC acids (SA) of the red blood cell (RBC) membrane are considered to play an important part in the physiology of the RBC1. There are indications that the amount of membrane sialic acid is a major factor in distinguishing young from aged RBC. Thus, ageing of circulating RBC is associated with a reduction of 20-30% SA which may be an important determinant of RBC survival2,3 in the eventual recognition and sequestration of the latter cells by the reticuloendothelial system2. During studies of thalassaemic RBC we observed, among other alterations, that the average level of SA was approximately 25% less than in normal RBC membranes obtained from healthy donors4. We, therefore, investigated the comparative ultra-structural distribution of SA on the surface of thalassaemic RBC membranes. We found that the SA residues on the surface of thalassaemic RBC are distributed in an uneven manner and are less abundant than those present on normal RBC surfaces.