It has been found that 3-(2,4-dichlorophenylazo)-9-(2,3-epoxypropane)carbazole can act as an efficient colourant and thermal stabilizer of poly(vinyl chloride) (PVC). It hinders evolution of hydrogen chloride, thus contributing to the stabilization of the system, probably via an aromatic alkylation reaction. Preliminary kinetic analysis supports the idea that the mechanism of dehydrochlorination is of polaron type and yields values of the activation energy, calculated by method of Ozawa-Flynn-Wall (for alpha = 0.5) in the range of 131.8-172.4 kJmol(-1). (C) 1997 Elsevier Science Ltd.