Hemin has been shown to disrupt erythrocyte membrane skeletal protein-protein interactions, initially those involving band 4.1 (Shaklai et. al. (1986) Biochem. Int. 13, 467-477). We have used electron spin resonance (ESR) spin labels specific for cell-surface carbohydrates, skeletal membrane proteins, or bilayer lipids to find: (1) simultaneous reaction of the protein-specific spin label, MAL-6, which binds to skeletal protein SH residues, and 10 microM hemin suggested that hemin decreased skeletal protein-protein interactions; (2) 10 microM hemin markedly decreased (greater than 60%, P less than 0.001) the rotational motion of spin-labeled erythrocyte membrane cell-surface sialic acid residues, 70% of which are located on the major transmembrane sialoglycoprotein, glycophorin A; and (3) 10 microM hemin caused a small, but significant (P less than 0.02), decrease in the motion of a lipid bilayer specific spin label (5-NS) in the erythrocyte membrane. Since glycophorin A is reportedly linked to the erythrocyte membrane skeletal protein network by band 4.1, it is conceivable that hemin-induced disruption of skeletal protein interactions, particularly those of band 4.1, could subsequently lead to the alterations in the motion of cell-surface sialic acid presented in this report.