Stabilized aqueous solution of a coenzyme for hydrogen-transferring enzymes characterized in that the solution contains NAD, NADP or a derivative thereof in an oxidized or reduced form and one or several organic compounds or salts thereof having a pKa value between 1.5 and 6.0 and/or a nitrogen compound of the general formula ##STR00001## in which the residues R.sub.1, R.sub.2 and R.sub.3 are the same or different and denote hydrogen, or a saturated or unsaturated alkyl or aryl group as well as the use of the solution to determine dehydrogenases in particular lactate dehydrogenase or substrates thereof.