Erythrocytes must have the capacity to undergo marked membrane deformation and shape changes in order to circulate through capillaries and respond to a range of shear stresses. To study the interrelationships between membrane deformability and the capacity for shape transformation, we created rigid membranes using several agents and then examined the ability of these erythrocytes with rigid membranes to undergo amphipath-induced shape change. We have previously shown that wheat germ agglutinin (WGA) and a monoclonal antibody to glycophorin A (R-10) cause membrane rigidity as measured by ektacytometry. Experiments were therefore designed to produced comparably rigid membranes using WGA, R-10, and diamide, and then to test the ability of lysophosphatidylcholine to produce echinocytes, and primaquine to produce stomatocytes. We found that diamide treatment substantially blocked both types of shape change. In contrast, R-10 binding did not impair either primaquine- or lysophosphatidylcholine-induce shape change. Further, WGA blocked echinocyte transformation, as previously reported, but not stomatocytosis. Using reduced and unreduced gel electrophoresis and Triton extraction, we compared the biochemical changes associated with WGA-, diamide-, and R-10-induced rigidity, and found them to be different. We conclude that not all rigid cells are incapable of shape change, and therefore that decreased membrane deformability is not predictive of impaired capacity for shape change.