Abstract On the basis of indirect experimental evidence, Scott and Bedford proposed about twenty years ago a mechanism of the accelerator action of metallic dithio-carbamates, known as the polysulfide theory. According to these authors, a metallic dithiocarbamate reacts with sulfur during vulcanization to form a polysulfide, which subsequently decomposes and liberates active sulfur for reaction with the rubber hydrocarbon. This theory gained support by the observation of Jones and Depew that the solubility of zinc dimethyldithiocarbamate in rubber is increased when sulfur is added to the mix, since such behavior may result from the formation of a soluble polysulfide. More recently, Scott and Sebrell questioned Scott and Bedford's polysulfide theory, on the basis that no polysulfides of metallic dithiocarbamates have been isolated. The author does not intend to enter into the controversial subject of the mode of action of vulcanization accelerators, but rather to present experimental data which confirms the original supposition of Scott and Bedford that sulfur forms unstable addition compounds, or polysulfides, with metallic dithiocarbamates. The metallic dithiocarbamates investigated were zinc diethyldithiocarbamate and zinc dibutyldithiocarbamate.