Some aspects of thermodegradation and stabilisation of flexible poly(vinyl chloride) (PVC) compounds have been studied by chemiluminescence (CL). The oxidation of PVC is shown to be chemiluminescent and the CL behaviour is sufficiently similar to that of a model polyene, ƒÒ-carotene, to suggest that the CL arises from the oxidation of polyenes formed by dehydrochlorination and that its intensity can be a measure of polyene formation. CL monitoring is shown to be useful in differentiating functionalities of different stabilizers in terms of their ability to retard polyene formation. Ba/Zn carboxylates which yield good initial or short-term colour stability at high temperatures or good low/moderate temperature stability by blocking of the propagating polyenes can easily be distinguished from stabilisers which do not retard polyene formation so well. The applicability of the CL technique in assistance with additive selection (e.g. HCl absorbers, phosphites) for providing a formulated compound with the required heat stability is demonstrated.