A developer for irradiated, radiation-sensitive recording materials, in particular for the production of offset printing plates, which contains water, a compound which is alkaline in aqueous solution and a copolymer which acts as an emulsifier and has units of (I) a hydrophobic vinyl compound which has alkyl radicals having up to 30 carbon atoms and (II) a hydrophilic, ethylenically unsaturated carboxylic acid. Some of the carboxyl groups of the copolymer are esterified with reaction products of (A) (C.sub.1 -C.sub.30)alkanols, (C.sub.8 -C.sub.25)alkanoic acids, (C.sub.1 -C.sub.12)alkylphenols or di(C.sub.1 -C.sub.20)alkylamines with (B) (C.sub.2 -C.sub.4)alkylene oxides or tetrahydrofuran.