Cellular swelling of erythrocytes exposed to Me2SO during freezing and thawing may lead to hemolysis upon dilution of the cryoprotectant with pure electrolyte buffer. Excessive cell swelling is effectively avoided by exposing the RBC to the nonpenetrating sorbitol after thawing and before dilution. Due to the initial reduction in volume by sorbitol, cell swelling upon dilution may not cause hemolysis particularly with concentrations of 0.05 to 0.15 M of sorbitol in the diluting electrolyte buffer. Membrane damage incurred during freezing and thawing is particularly pronounced with the older red cell population, while the younger population membrane integrity can be preserved to an optimal degree.