Doping of polyacetylene with arsenic pentafluoride is found to involve oxidation of the polymer according to the mechanism: 2(CH)x + 3AsF5 → 2(CH)+x + 2AsF-6 + AsF3. The AsF-6 ions intercalate beteeen the polymer chains in a nonrandom fashion. Oxidation of the polymer is accompanied by replacement of the original interband transition in the visible by a featureless transition extending into the infrared. Treatment of the doped polyacetylene with ammonia destroys the enhanced conductivity and regenerates a visible spectrum similar to that of the undoped polymer but somewhat blue-shifted. Possible explanations are offered for these results in terms of the proposed mechanism of doping. © 1979.