Compounds of the general formula (1) ##STR1## in which the Zs, preferably identical to each other, each denote a hydroxy group or a sulfato, thiosulfato or phosphato group. They can be prepared by first converting biphenyl by sulfochlorination into biphenyl-4,4'-disulfochloride, then reducing the latter with an alkali metal or alkaline earth metal sulfite or hydrogensulfite to sulfinic acid, and in turn reacting the latter with ethylene oxide to give 4,4'-bis-(.beta.-hydroxyethylsulfonyl)-biphenyl, which can be esterified in conventional manner. They are used for modifying and improving the physical and coloristic properties of materials made of natural and/or synthetic polyamide fibers and/or polyurethane fibers and as auxiliaries in dyeing processes for such fiber materials.