Near infra-red spectroscopy (NIR) can be used to analyze the concentrations of all the components of a PVC mixture. Unlike conventional methods for the analysis of mixtures, this technique is not limited to one ＇＇critical＇＇ component. The stabilizer is most readily dispersed in the mixture and is not, as often assumed, the ＇＇critical＇＇ component.