PURPOSE: To obtain the subject fiber, produced by wet spinning, and subsequently drying, a mixture of specific element and long-chain synthetic polymer in a solution, X-ray detectable and useful for, e.g. artificial ligaments.

CONSTITUTION: This fiber having an elongation of 300% or more is obtained by the steps of (1) dissolving a long-chain synthetic polymer containing at least 85 wt.% of segmented polyurethane (A) in an organic solvent (B), e.g. dimethylacetoamide, (2) incorporating the above solution with an X-ray nontransmittable filler containing an element having an atomic number of 20 or more (e.g. barium sulfate) preferably at 25 to 55 wt.%, based on the total solids, (3) wet or air-gap spinning the above solution, and (4) solidifying the resultant fibers by a water bath.