When cheddar cheese whey was treated under the optimized conditions, i.e., 1.33 mg/mL sodium hexametaphosphate (SHMP) at pH 4.07 and 22°C for 1 hr, more than 80% of P-lactoglobulin was removed by precipitation. In the supernatant, almost all of the immunoglobulins and the major portion of a-lactalbumin were retained, as indicated by SDS gel electrophoresis. Immunochemical assays showed that approximately 90% of immunoglobulin G activity was found in the supernatant. By dialysis against water for 48 hr, 72.2% and 45.3% phosphorous was removed from the supernatant and precipitate, respectively.