N-terminal analysis of the proteins extracted from ox (Bos taurus) erythrocyte membranes by dilute EDTA is used as a means of estimating the heterogeneity of the protein fractions. Dinitrophenylation and dansylation reveal up to 8 different N-terminal amino acids in fractions with electrophoresis after dodecylsulphate treatment shows as having far fewer polypeptide chains. These fractions are prepared by gel electrophoresis in the presence and absense of detergent. Molecular weight estimation by the Ferguson procedure of the components revealed in the EDTA extract by electrophoresis in the absence of detergent confirms the large size concluded from electrophoresis with dodecylsulphate. The N-terminal analyses indicate that the high molecular weight of the complexes, both in the presence and absence of detergent, is more probably due to their being complexes of several polypeptides than exceptionally long single polypeptide chains.