Evaluation of erythrocytes from patients with hereditary hydrocytosis and from healthy donors by ektacytometry. (A) Whole cell deformability was measured by subjecting isotonic erythrocytes to increasing shear stress. (B) Osmotic deformability was measured by subjecting erythrocytes to moderate shear stress while increasing osmotic pressure. The data shown were highly similar in 2 experiments conducted on the patients' blood collected on 2 separate occasions.