The effects of N,N -bisdimethyl-1,2-ethanediamine dichloride (dioctyldiQAS), a double chain surfactant with two positive charges in the polar head, on the erythrocyte membrane were studied. At sublytic concentrations dioctyldiQAS protected erythrocytes against hypotonic hemolysis, induced the formation of sphero-echinocytes, increased passive fluxes of potassium through the membrane, decreased the activity of the Na + -K + -pump and decreased the efflux of phosphate. The alterations in membrane-connected functions induced by dioctyldiQAS are qualitatively similar to those induced by its single-chain close analogue decyltrimethylammonium bromide. DioctyldiQAS, however, exhibited these effects at considerably lower concentrations than decyltrimethylammonium bromide. This is most likely due to a higher extent of partitioning into the membrane by dioctyldiQAS.