Disclosed is a composition including IL-6, an isoform or a fragment thereof, a compound of the formula C10-C18-alkyl trimethylammonium halogenide (I), wherein the compound is saturated or unsaturated and/or substituted or unsubstituted, or a salt thereof, wherein the concentration of the compound in the composition is about 0.15 to about 0.4%, and a serum. Also disclosed is a kit including a composition or a lyophilisate and instructions for use. A further embodiment of the present invention is method of stabilizing IL-6, an isoform or a fragment thereof, including the steps of mixing IL-6, an isoform or a fragment thereof, a compound of the formula C10-C18-alkyl trimethylammonium halogenide (I), wherein the compound is saturated or unsaturated and/or substituted or unsubstituted, or a salt thereof, wherein the concentration of the compound in the composition is about 0.15 to about 0.4%, and a serum.
