A spectrophotofluorometer, suitably modified for use with plastics films, was used to study a series of cellulosic polymer films. The chemical structure of the films was found to be related to the wavelength and intensity of the fluorescence emission spectra. Saturated aliphatic esters and ethers were found to possess strong fluorescence maxima at about 350 mμ. Cellulose nitrate exhibits very weak fluorescence at 310 mμ, and a moderate fluorescence maximum appears at 440 mμ for cellulose derivatives containing double bonds or carboxyl groups. A series of experiments is described in which the modification of chemical structure was followed by measuring changes in fluorescence spectra.