The tendency of polymers of sickled hemoglobin (HbS) to align parallel and equidistant to each other has been pointed out in many investigations, and is considered a characteristic feature of erythrocyte sickling. A previous study on stroma-free solutions of sickled hemoglobin, however, suggested that polymers of HbS preferentially assumed radial rather than parallel relationships. Sickled erythrocytes were exposed to hypertonic stress in the present study in order to observe whether parallel bundles of polymers remained intact after removal of the cell membrane. Bundles of polymers in salicylate damaged sickled cells regularly developed branching and radial configurations similar to those found in stroma-free gels. Rotational stress appears to be the dominant factor influencing the relationship of HbS polymers, and the force generated by that tension may be an important factor in erythrocyte sickling.