The autoöxidation of rubber is sensitive to the action of catalysis; anti-oxygenic compounds are antagonistic to the process and retard its progress; proöxygenic compounds on the contrary promote autoöxidation, and in their presence the effects of autoöxidation are evident sooner. In the present paper, experiments are described, the object of which was to study the action of a few typical proöxygenic compounds on rubber hydrocarbon. Among the substances which accelerate the action of oxygen, certain salts of copper, iron, cobalt, and manganese are known to be very active. Various organic derivatives of these metals were studied in the present work, including (1) copper acetylacetonate, oleate, linoleate, sulforicinoleate, elaidate, stearate, enanthate, pelargonate, hendecenate, erucate, and diethylthioneethiolcarbamate; (2) iron acetylacetonate, oleate, linoleate, sulforicinoleate, and pelargonate, and the dibenzoylmethane derivative of iron; (3) cobaltous oleate, linoleate and sulforicinoleate, and cobaltic acetylacetonate; (4) manganous oleate, linoleate, sulforicinoleate and pelargonate, and manganic acetylacetonate. A study was also made of certain more complex metal derivatives, including salts of the dithizone of cupferron, of mercaptobenzothiazole, of α-nitrose-β-naphthol, of benzyldioxime, etc. The method followed involved two steps: (1) incorporation of a predetermined percentage of a proöxygenic metal compound into samples of vulcanized rubber, (2) estimation of the acceleration of autoöxidation induced by the particular proöxygenic compound. In the first step, the rubber sample was cut into small cubical pieces 2–3 mm. on a side, and these were placed in a chloroform solution of the particular salt under investigation. The average content of proöxygenic compound which was absorbed was about 0.1 per cent. The swelling of the rubber in the solution was the determinant factor in the total amount of proöxygenic compound and solvent which were absorbed.