An improved process is provided for the production of polymeric filamentary material or film. Molten melt-spinnable polymeric material capable of undergoing crystallization (e.g., a polyester) is extruded through a shaped orifice to form a filamentary material or film under high stress conditions, quenched to below its glass transition temperature to form a solid filamentary material or film, and sequentially passed for a brief residence time through a thermal conditioning zone at a temperature between its glass transition temperature and its melting temperature wherein the internal structure thereof is modified and substantial crystallization of the previously solidified filamentary material or film takes place. The filamentary material or film is withdrawn from the conditioning zone at a rate of 1000 to 6000 meters per minute while under a relatively high stress of about 0.1 to 1.0 gram per denier. The process is conducted while exerting a constant tension upon the filamentary material or film in the absence of stress isolation. The melt extrusion process yields a product wherein the tensile strength and modulus are improved and the shrinkage characteristics are diminished.