Under the influence of the UV light in 2-aryl substituted benzothiazoles doped PVC films take shapes. a new pseudophotochromic system. The coloured films were formed by two processes - the liberation of HCl during the photodegradation of PVC and an interaction between HCl and 2-arylsubstituted benzohiazoles (BT). They can return thermally to the colourless films and this process depends on the stability of the complexes BTH+.Cl-. Reversible photochromism was observed in the films on repeating irradiation with UV light. The experimental results, possible applications and future work on this pseudophotochromic system are also discussed.