A method is proposed for operating a metering valve which is realized as a solenoid valve which is actuated by an electromagnet that interacts with an armature which is connected fixedly to a valve needle and, furthermore, is loaded with a pulse-width modulated metering signal which defines the metering of a reagent which is to be introduced into the exhaust-gas region of an internal combustion engine or of a preliminary stage of a reagent, as is an apparatus for carrying out the method. The opening duration of the metering valve is limited to a minimum opening duration, for which the metering valve is opened completely and which is fixed in such a way that a spray mist is always produced during the metering. The procedure according to this invention prevents the reagent from crystallizing and, as a result, firstly ensures exact metering of the reagent and secondly counteracts clogging of the metering valve, in particular if a urea/water solution is provided as preliminary stage of the reagent.