This invention describes high-strength fibers with high initial moduli from homopolymers or copolymers comprising at least 70% by weight repeating acrylonitrile and/or methacrylonitrile units, and a process especially adapted for their preparation, and their use, especially as reinforcing materials or for producing filters or friction coatings. The fibers according to the invention have a strength of more than 100 cN/tex and an initial modulus of more than 15 N/tex (based on 100% elongation).