Purification method interferon-beta.

A method for preparing a composition comprising interferon-beta (IFN-beta) monomer, which method comprises: a) preparing a sample comprising purified IFN-beta; b) mixing said sample with hydrochloride (HCl) guanidine to obtain a first solution comprising IFN-beta solubilized denatured; and c) renaturing said IFN-beta by dilution of said first solution with a first buffer, wherein said first buffer has a pH of 3.0 to 5.0, and wherein a solution of IFN-beta is obtained renatured that It comprising IFN-beta monomer and residual HCl gunidina.