Recent developments in EPDM production technology have led to improved control of polymer structure because they have made it possible to control the level of long chain branching. This has resulted in a new generation of EPDM polymers, which are currently being introduced in the market. In the late eighties, DSM developed an advanced analytical method for quantifiying the level of long chain branching. Using this method, by means of dynamic mechanical spectrometry a rheological fingerprint of the EPDM polymer structure is obtained, from which the level of long chain branching can be derived. In a production environment, however, this novel method will be of limited use. Therefore the Mooney Stress Relaxation test has been studied as an alternative method for quantifying polymer structure in terms of (controlled) long chain branching of EPDM polymers.