This International Standard specifies a direct spectrometric method for the determination at 450 nm of the smoke condensate retention index of a cigarette filter. The method is applicable to filter cigarettes. It is not applicable to cigarettes with coloured filters or to cigarettes with filters containing special additives, for example alkaline additives or absorbents such as active charcoal. This empirical, quick and practical method relates only to smoke condensate. The results should not be interpreted with respect to any particular constituent of the smoke condensate.