ENDOR measurements have been carried out on trans-polyacetylene and on 0.5 mol % ReF6 doped 70% cis-polyacetylene at 4 K. The pure trans-polyacetylene yields only a single line, but the ReF6 doped material yields two hyperfine couplings to hydrogens of 0.2 and 1.7 MHz. Calculations suggest the average chain length of the soliton is 93 carbon atoms. The absence of fluorine hyperfine coupling suggests that ReFn molecular units are in the C, H molecular plane of the trans-polyacetylene.