Beta-Cyclodextrin (beta-CyD) significantly protected the human erythrocytes from hemolysis and shape changes induced with chlorpromazine and flufenamic acid in isotonic solution. A good correlation between the stability constants of inclusion complexes (beta- greater than gamma- greater than alpha-CyD) and the inhibitory effects on drug-induced hemolysis was found. From the observations of drug uptake into erythrocytes and changes in surface tension, the protective effects of CyDs appeared to be due to the decrease in effective concentration of drug through inclusion complexation rather than the direct interaction of CyDs with erythrocyte membrane.