Abstract: A process and apparatus for heating injected, cold preform blanks composed of partly crystalline synthetic resins which have been produced by injection molding. The preform blanks are positioned in holders on a conveyor and are rotated about their longitudinal axes as they are moved along the conveyor, heated to blow mold temperature in multiple stages including a series of heating and cooling stations on respective opposite sides of the conveyor so as to be heated from one side of the conveyor and cooled from the other side while being carried on the conveyor and while being simultaneously rotated whereby they are uniformally heated across their cross sections. The process is completed by tempering and producing a protective surface on the preform blanks before they are supplied to a blow molding device. The entire process requires only several minutes of time.