The present invention concerns a process for the purification of EPI-HNE proteins, from the culture medium of a host strain for the expression of said proteins, comprising the steps of: (a) passing a derived part of the culture medium over an expanded bed of cationic exchange adsorbent or a mechanically and chemically inert micromembrane, in order to recover an eluate, (b) optionally conducting chromatographic separation of proteins, according to their hydrophobicity, on the resulting eluate, (c) passing the resulting eluate over a cationic exchange column, (d) optionally filtering the resulting medium such as to obtain a sterile filtrate, and optionally further comprising the step of (e) causing precipitation of EPI-HNE in a crystallised form and recovering the protein crystals.