This paper presents some further work on a thermodynamic investigation of polymer solutions which may be considered to have begun with studies on a typical polar polymer, polyvinyl chloride (4, 5); the present work is based on polystyrene as a representative of the class of non-polar polymers. Here we deal chiefly with the effect of structural features and temperature on the osmotic pressure of dilute polystyrene solutions. A more comprehensive investigation, including a study of concentrated solutions, has been completed (15) and will be published later.