Method of purifying a protein from a solution of substances comprising the steps of passing the solution through an ion exchange material at a pH which facilitates binding of the protein of interest, washing the bound protein at a different pH at which the bound protein does not elute but which the free protein would not bind to the ion exchange material, and then eluting the protein at a pH which facilitates elution. Method is especially useful in purification of antibodies such as antibodies to tumor necrosis factor.
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