The evanescent and scattered light from poly(styrene) thin film waveguides are being investigated to evaluate the potential use of integrated optic waveguides as sensors. A fiber optic system is described for measuring the light intensity of different waveguide modes in two directions; perpendicular to the waveguide streak and parallel to the streak as a measure of decay. Rayleigh and poly(styrene) Raman scattered light are used as intensity indicators and the advantages and disadvantages of each are discussed. Profiles of Raman scattered light across the waveguide streak are shown as a function of position along the waveguide. Decay measurements of four waveguide modes along a single waveguide are divided into three regions with different rates of decay and possible causes. These results show that the excitation field along the surface of 10 waveguides is predominantly scattered light rather than surface localized evanescent light. © SPIE.