Abstract: A process for the preparation of thermoplastic fibers which comprises:(a) spinning a solution of an alternating copolymer of an olefinically unsaturated compound and carbon monoxide, having a number average molecular weight of at least 5000, to fibers through a spinning aperture, said solution having a polymer content in the range of from 0.1-50% m(b) submitting the thus obtained fibers to a solvent-removal treatment to remove substantially all the solvent, and(c) stretching the thus obtained substantially solvent-free fibers in an environment having a temperature between the glass-transition temperature of said polymer and (T+20).degree. C., when T is the crystalline melting point of the polymer.