Diffuse Interstellar Bands (DIB) are broad absorption bands in the visual and near-IR spectrum of stars behind diffuse clouds. The absorptions are thought to be due to electronic transitions in large molecules, but the specific molecules have not been identified. The absorbed energy will be emitted in the mid infrared. A direkt link with the Unidentified Infrared Bands (UIB) is suggested, but has not been established. We propose to test this hypothesis by measuring the relative band ratios of UIBs for lines of sight with significantly varying diffuse interstellar band spectra. If variations in the DIB spectrum reflect abundance variations of the carrier, then there should be a direct correlation between DIB spectrum and UIB spectrum. We propose to measure the UIB spectrum with ISOPHOT-S in a number of lines of sight in astrophysical environments that are very similar but show pronounced differences in the DIB spectrum.