The conversion of long slender filaments of Bi‐based high‐temperature superconductors from the amorphous to the crystalline phase has been studied in order to determine the suitability of these fibers for use in a multifilamentary magnet conductor. For very fine filaments, coarsening may be a problem, so special emphasis was placed on the optimum values of time and temperature used for recrystallization. Amorphous fibers approximately 1 &mgr;m in diameter can be crystallized to form granular filaments about 0.2 &mgr;m thick (in thecdirection) and 3 to 4 &mgr;m wide. Thecaxis generally grows perpendicular to the long axis of the fiber.