In the present study, we investigated the interaction of the non-ionic surfactants polyoxyethylene alkyl ethers (CnEm) with erythrocyte membranes. For this purpose we have performed hemolytic assays under isosmotic conditions with five surfactants in the 8 polyoxyethylene ether series. By applying to the hemolytic curves a quantitative treatment developed for the study of surface-active compounds on biomembranes, we could calculate the surfactant/lipid molar ratios for the onset of hemolysis (R-e(sat)) and for complete hemolysis (R-e(sol)). This approach also allowed the calculation of the binding constants for each surfactant to the erythrocyte membrane. Results in the C,,E series were compared to those obtained for Triton X-100, a well-known non-ionic surfactant with values of cmc and HLB in the range of the alkyl ethers studied. Inside the series the lytic effect increased with the more hydrophobic homologues (C10E8 < C12E8 < C14E8 < C16E8 < C18E8), with Re values between 3:1 and 0.03:1. The effect of C10E8 and C12E8 was found to be in the range of that caused by Triton X-100, proving that C,,E surfactants are strongly hemolytic. (C) 2002 Elsevier Science B.V. All rights reserved.9714554