The steady-state levels of β-spectrin phosphorylation in HbH (α-thalassemia 1/α-thalassemia 2), HbH/HbConstant Spring (α-thalassemia 1/HbCS, hereafter called HbH/HbCS) and nonsplenectomized β-thalassemia/HbE (hereafter called β-thal/HbE) red cells were quantitated using Western hybridization. Phosphorylation of β-spectrin serine and threonine residues from thalassemic samples was not significantly different from normal control. However, tyrosine phosphorylation was higher than normal control in HbH (p<0.01), HbH/HbCS (p<0.05) and β-thal/HbE (p<0.05) samples. Tyrosine phosphorylation of β-spectrin was observed only in the presence of vanadate, a phenomenon not hitherto reported. As tyrosine kinase activity has been linked to oxidative stress, loss of membrane lipid asymmetry and procoagulant activity of the red cell membrane, the observed increase in β-spectrin tyrosine phosphorylation of the thalassemic red cells is likely, at least in part, to account for these parameters.