AbstractThe volumes of human erythrocytes suspended in solutions of varying concentrations of sodium chloride and sucrose were measured by a Coulter Channelyzer® Model H4 with appropriate corrections. The cells showed greatly restricted volume changes at osmolarities between 200–700 mOsm. At osmolarities outside this limit, on the other hand, the cells showed nonrestricted volume changes following essentially the predictions of an ideal osmometer. This unexpected volume response was not spuriously due to changes in shape or to a changing orientation of the cells as they traversed the aperture. The restricted volume change observed was abolished when the cells had previously been treated with diamide or had been heated for 60 minutes at 50°C, conditions that are known to disturb the spectrin‐actin network. The possibility must be considered that the osmotic behavior of human erythrocytes may be nonideal and that this nonideal behavior is primarily due to mechanical restriction provided by the spectrin‐actin network of the membrane cytos
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