Water, carbon dioxide, and condensable condensate produced during the oxidation of polyisoprene popcorn polymer were determined gravimetrically. For pure polyisoprene popcorn polymer from which 4.6% soluble polymer and volatiles were removed, the rates of water and carbon dioxide production during the early stages of the autoxidation were linear and amounted to approximately 2 moles of water and 0.2 moles of carbon dioxide for every 10 moles of oxygen reacted.