The removal from human erythrocytes of cholesterol (mass) and of [3H]cholesterol which was introduced into the erythrocyte by exchange was studied. Removal was accomplished by incubating erythrocytes in plasma, the free cholesterol content of which was lowered by the action of lecithin:cholesterol acyltransferase. The exchange of cholesterol between erythrocytes and plasma and the net movement of cholesterol out of the membrane into plasma are characterized by the same rate constant and are driven by cholesterol to phospholipid ratios in cells and plasma. The apparent limitation on cholesterol depletion of erythrocytes observed in experiments of this type is explicable as the result of equilibrium between cholesterol in the membrane and in the plasma, an equilibrium reached when there is still cholesterol left in the cells. All the exchangeable cholesterol in human erythrocytes is apparently available for removal from the membrane.