THE chemical modification of proteins with succinic anhydride was shown by Habeeb et al.1 to result in an unfolding of the compact conformations of several proteins in neutral aqueous buffer. This was attributed to the large increase in net negative charge produced by the replacement of the positively charged e-NH3+ groups of lysine residues by negatively charged-NHCOCH2CH2COO-groups. An intensive study of the specificity of this reaction and of its conformational effects was made by Cherry2 with the protein bovine serum albumin; the results have been briefly reported3. Utilizing these findings, Klotz and Keresztes-Nagy4 made the interesting observation that the electrostatic repulsions introduced by succinylation could result in the complete dissociation of non-covalently linked sub-units of proteins, in particular, those of haemerythrin, at neutral pH without the addition of any other dissociating agents such as urea or detergent. We have now shown that rabbit γ-globulin, succinylated either before or after partial reduction of interchain disulphide bonds5, can be separated into its constituent heavy and light peptide chains5,6 by gel-filtration in aqueous buffers at pH near neutrality without the use of detergents7. Furthermore, the isolated succinylated heavy and light chains are quite soluble in such buffers, whereas isolated but unmodified heavy chains are insoluble6.