1. NR and IR vulcanizates can be distinguished from one another by their DSC and DTG curves. 2. Thermal curves remain more or less unaffected by recipe changes. 3. Identification of blends of NR and IR is complicated since different IR's have different exotherm areas. 4. Natural and synthetic trans-polyisoprenes can be distinguished from one another, as well as from their cis counterparts, by their DSC and DTG curves. 5. Differences observed in the natural and synthetic polyisoprenes seem to be due to a higher amount of cyclized product, formed as a result of catalysis by the residual inorganic material in the synthetic product.