An investigation has been performed to determine the mechanism by which dye solutes specifically interact in an amorphous copolyester matrix. Using FTi.r. spectroscopy it has been possible to determine both the type and strength of interactions that occur between dyes containing hydroxyl groups and a copolyester containing electron-donating carboxyl functional groups. Dye-polymer intermolecular interactions, dye-dye self-association intermolecular interactions and dye intramolecular interactions have been identified. The dye structures were simplified and changed systematically, enabling the effects of solute concentration, the number of solute hydroxyl groups and the flexibility of the solute molecule to be established on the various interactions.