The purpose of the present invention is to provide a water-soluble tetrazolium compound that will form a water-soluble formazan exhibiting long-wavelength absorption and is stable in aqueous solution for a long period and suitable for the quantitative analysis of dehydrogenases or substrates thereof. Disclosed is a water soluble tetrazolium compound expressed by the following general formula (1): ##STR00001## wherein each of R.sup.1 to R.sup.19 independently represents hydrogen atom; nitro group; sulfonate group or alkyl, alkoxy, sulfoalkyl or sulfoalkyloxy groups having 1 to 4 carbon atoms; provided that each of at least two of R.sup.1 to R.sup.19 independently represents sulfonate group; or sulfoalkyl or sulfoalkyloxy groups having 1 to 4 carbon atoms; and M represents an alkali metal or ammonium ion.