We present a technique to synthesize high aspect ratio metallic nanostructures based on the radiolysis method. In our experiments, we use gamma rays to irradiate aqueous solutions containing Ag and Pt ions and a water-soluble polymer. The aspect ratio of the nanoparticles is controlled by varying the radiation dose rate, the type of polymer, and the type of counter ions. Transmission electron microscopy shows that wire-like structures composed of grains with a face centered cubic (fcc) structure can be formed with a length of up to 3.5μm and typical diameters between 5 and 12nm. X-Ray absorption spectroscopy shows that Ag and Pt do not form an alloy, but remain segregated.