Abstract: A method of dehydrogenating alkylaromatic compounds to produce vinylaromatic monomers wherein an alkylaromatic compound feed stream is preheated by passing it in indirect heat exchange relation with steam, the preheated feed stream is then flash vaporized by injecting superheated steam therein, the feed vapors are then passed in indirect heat exchange relation with hot effluent vapors withdrawn from the dehydrogenation reaction zone, after which the hot alkylaromatic compound vapors are introduced, together with superheated steam into a dehydrogenation reaction zone containing a bed of alkylaromatic compound dehydrogenation catalyst and reacted to produce a vinylaromatic compound containing effluent stream which is withdrawn from the reaction zone, passed in heat exchange relation with the incoming alkylaromatic compound feed and condensed.