In one aspect, the invention is directed to a composition comprising IL-6, an isoform or a fragment thereof, a compound of the formula C10 - C18-Alkyl trimethylamonium halogenide (1), wherein the compound is saturated or unsaturated and / or substituted or non substituted, or a salt thereof, wherein the concentration of the compound in the composition is about 0.15 - about 0.4%, and a serum.The present invention is further directed to a kit comprising a composition or a lyophilisate and an instruction for use. A further embodiment of the present invention is method of stabilizing IL-6, an isoform or a fragment thereof, comprising the steps of mixing IL-6, an isoform or a fragment thereof, a compound of the formula C10 - C18-Alkyl trimethylamonium halogenide (I), wherein the compound is saturated or unsaturated and / or substituted or non substituted, or a salt thereof, wherein the concentration of the compound in the composition is about 0.15 - about 0.4%, and a serum.
