Excessive binding of possible autoantibodies to discrete subpopulations of circulating sickle erythrocytes has been documented. However, the mechanism by which putative autoantibody binding sites selectively develop on sickle cells is unknown. In the present study, autologous IgG binding has been quantified for low density sickle erythrocytes subjected to prolonged morphologic sickling under nitrogen in the absence of plasma (24 hours, 37 degrees C), and to reoxygenation with subsequent incubations in varying dilutions of autologous plasma. Cell-bound IgG was measured using a nonequilibrium 125-iodinated protein-A-binding assay. Binding isotherms show that IgG binding was both concentration dependent and saturable. Sickle cells pretreated by deoxygenation exhibited approximately 2-fold increased saturation binding of autologous IgG as compared with oxygenated paired samples, suggesting that new autoantibody binding sites may have developed during prolonged sickling. Autologous IgG binding to sickle cells pretreated by deoxygenation was also inhibited 2-fold more by limiting quantities of deoxygenated autologous cells, as compared with inhibition by oxygenated sickle erythrocytes used for serum absorption. These findings indicate that the sickling-associated increase in IgG binding may represent an increase in specific autoantibody binding sites, and suggests that autoantibody binding sites are produced by permanent sickling-associated remodeling of the red cell surface.