The extent of binding of sodium dodecyl sulphate to bovine serum albumin at high binding ratios was investigated by gel filtration. The weight ratio of bound sodium dodecyl sulphate to bovine serum albumin increases with the NaCl concentration, and, except at low salt concentrations, with the concentration of sodium dodecyl sulphate. In the presence of 1.0g of sodium dodecyl sulphate/l, the binding ratio varied from 1.0 (at 0.04m-Na+) to 2.2 (at 0.44m-Na+). In the presence of 0.24m-Na+, the binding ratio increased with sodium dodecyl sulphate concentration, from 0.9 (0.2g of sodium dodecyl sulphate/l) to 2.0 (5g of sodium dodecyl sulphate/l), at 26°C, in a dilute sodium phosphate buffer. No significant dependence of the binding ratio upon temperature in the range 26–45°C was observed. These results differ from those of Reynolds & Tanford (1970a) obtained by equilibrium dialysis.
